แบบฝึกหัด เรื่อง สมการเชิงเส้นตัวแปรเดียว

1 โรงเรยี นสีคิว้ “สวัสด์ผิ ดงุ วทิ ยา” แบบฝกึ หัด/ใบงาน กลมุ่ สาระการเรียนรู้ คณิตศาสตร์ รายวิชา คณติ ศาสตร์ 2 เร่ือง สมการเชงิ เส้นตวั แปรเดียว ชนั้ มัธยมศึกษาปีท่ี 1 รหัสวชิ า ค21102 ผสู้ อน ครสู มพร ขวัญสันเทียะ หน่วยการเรียนรู้ท่ี 1 ช่ือนกั เรยี น..............................................................................................ชั้น ม...../........ เลขที่......................... แบบฝึกหดั 1.1 การหาคา่ ของนพิ จน์พชี คณติ จงหาคา่ ของนพิ จนพ์ ชี คณิตต่อไปนี้ 1. 120(r + 40) เมือ่ r = 10 2. (5a + 4)(25a) เมือ่ a = 4 วิธีทำ ........................................................................ วิธีทำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 3. (3xy + 45) - 75 เม่ือ x = 10 และ y = -2 4. 3m3 + 23 เม่ือ m = 4 วิธีทำ ........................................................................ วิธที ำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 5. 1 (75p − 520) เมือ่ p = -20 6. 4y2 −10 เมอื่ y = 5 2 5 วธิ ที ำ ........................................................................ วธิ ที ำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. ..................................................................................

2 แบบฝึกหดั 1.1 ข การเขียนนพิ จนพ์ ชี คณิต 1. จงเขยี นนิพจนต์ ่อไปน้ีให้อยใู่ นรปู อย่างงา่ ย 1) 3x + 4x = …………………………………………………………………………………………………….. 2) 2a – a = …………………………………………………………………………………………………….. 3) 7a + 2a + 3a = …………………………………………………………………………………………………….. 4) 5x – 4x + 8x = …………………………………………………………………………………………………….. 5) 10m + 6m – m = …………………………………………………………………………………………………….. 6) 11a + 5a + 7 – 4 = …………………………………………………………………………………………………….. = …………………………………………………………………………………………………….. 7) 16x – 4x – 10 + 3 = …………………………………………………………………………………………………….. = …………………………………………………………………………………………………….. 8) 1 x + 1 x − x = …………………………………………………………………………………………………….. = …………………………………………………………………………………………………….. 24 2. จงกระจายนิพจน์ตอ่ ไปนี้โดยใชส้ มบัตกิ ารแจกแจง 1) 5(x + 1) = …………………………………………………………………………………………………….. 2) 2(3m + 2) = …………………………………………………………………………………………………….. 3) -4(y + 8) = …………………………………………………………………………………………………….. 4) -2(a - 5) = …………………………………………………………………………………………………….. 5) 10(8 - x) = …………………………………………………………………………………………………….. 6) 6(11 – 2x) = …………………………………………………………………………………………………….. 7) -3(10 - m) = …………………………………………………………………………………………………….. 8) -5(8 – 2a) = …………………………………………………………………………………………………….. 3. จงเขียนนพิ จนแ์ ทนข้อความทีก่ ำหนดให้ต่อไปนี้ให้ 1) จำนวนซึง่ มากกว่า t อยู่ 250 ตอบ ………………………………………………………………… 2) จำนวนซ่งึ น้อยกว่า 56 อยู่ a ตอบ ………………………………………………………………… 3) ผลบวกของ 5 เท่าของ x กบั 6 ตอบ ………………………………………………………………… 4) หกเท่าของผลบวกของ m กบั 115 ตอบ ………………………………………………………………… 5) ครึง่ หนงึ่ ของผลบวกของ n กบั 80 ตอบ ………………………………………………………………… 6) สามในห้าของสองเท่าของผลตา่ งของ y กบั 9 ตอบ ………………………………………………………………… 7) แปดเทา่ ของจำนวนจำนวนหน่งึ รวมกบั อีกหน่ึงในแปดของจำนวนจำนวนนนั้ ตอบ ………………………………………………………………………………………………………………………………………… 8) ผลตา่ งของจำนวนจำนวนหนงึ่ กบั 7 หารดว้ ย 12 ตอบ ………………………………………………………………………………………………………………………………………… 9) ผลบวกของจำนวนเตม็ สองจำนวนทเ่ี รยี งกนั ตอบ ………………………………………………………………………………………………………………………………………… 10) ผลบวกของจำนวนคี่สามจำนวนทีเ่ รยี งตดิ กนั ตอบ …………………………………………………………………………………………………………………………………………

3 แบบฝกึ หดั 1.2 สมการและคำตอบของสมการ 1. จงตรวจสอบวา่ จำนวนท่ใี หไ้ วใ้ น [ ] เปน็ คำตอบของสมการท่กี ำหนดให้หรอื ไม่ 1. z – 3 = 7 [10] 2. 7 – k = 2 [0] วิธที ำ ........................................................................ วิธีทำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 3. -2 = -15 – m [13] 4. -27 = x – 18 [-9] วธิ ที ำ ........................................................................ วธิ ที ำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. ................................................................................... .................................................................................. 5. 1.2 + b = 4.8 [3.6] 6. 3 = m − 1 [2] วิธที ำ ........................................................................ 22 .................................................................................. วิธีทำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 7. -24y = 168 [-7] 8. c = 6 [180] วิธที ำ ........................................................................ − 30 .................................................................................. วิธที ำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 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4 2. จงหาคำตอบของสมการตอ่ ไปนี้ โดยวิธลี องแทนคา่ ตัวแปร 1. a + 3 = 2 2. 2b = 15 วธิ ที ำ ........................................................................ วธิ ีทำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 3. s − 1 = 0 4. 7c + 6 = -1 7 วิธีทำ ........................................................................ .................................................................................. วธิ ที ำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. ................................................................................... 5. 2 y = −2 6. z3 = -1,000 วิธีทำ ........................................................................ 3 .................................................................................. .................................................................................. วิธที ำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 7. 5x2 = 20 8. m + 3 = m วิธที ำ ........................................................................ วิธีทำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 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5 3. จงเขียนสมการแสดงความสัมพนั ธท์ ี่กำหนดให้ในแต่ละขอ้ แล้วหาคำตอบโดยวิธีลองแทนค่าตวั แปร 1. x ลบดว้ ย 11 เทา่ กับ -5 2. จำนวนซ่ึงน้อยกว่า x อยู่ 6 คือ 15 วธิ ีทำ ........................................................................ วิธที ำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. ……………………………………………………………………….. 3. จำนวนซง่ึ มากกวา่ x อยู่ 3 คอื 16 4. สามเท่าของ y เทา่ กับ -9 วธิ ที ำ ........................................................................ วธิ ีทำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. ................................................................................... .................................................................................. ................................................................................... .................................................................................. 5. ผลบวกของ y กบั สามเทา่ ของ y เท่ากับ 20 6. จำนวนจำนวนหนงึ่ หารด้วย 5 แลว้ ผลหารเท่ากับ 20 วธิ ีทำ ........................................................................ วธิ ีทำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 7. สองเทา่ ของจำนวนจำนวนหนง่ึ กบั อกี 3 8. คร่ึงหน่ึงของจำนวนจำนวนหนง่ึ น้อยกวา่ 22 อยู่ 14 มีค่าเท่ากับ 33 วธิ ที ำ ........................................................................ วธิ ีทำ ........................................................................ .................................................................................. 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6 แบบฝึกหัด 1.3 ก การแกส้ มการเชงิ เส้นตวั แปรเดยี ว สมบัติสมมาตร (symmetric property) ถา้ a = b แลว้ b = a เม่อื a และ b แทนจำนวนใดๆ เช่น ถ้า x = 8 แล้วจะสรปุ ไดว้ า่ 8 = x สมบัติถ่ายทอด (transitive property) ถา้ a = b และ b = c แล้ว a = c เมอ่ื a, b และ c แทนจำนวนใดๆ เชน่ ถา้ x = y และ y = 3 แล้วจะสรปุ ได้วา่ x = 3 สมบตั ขิ องการเท่ากนั เกยี่ วกับการบวก ถา้ a = b แล้ว a + c = b + c เมอื่ a, b และ c แทนจำนวนใดๆ (additive property of equality) เชน่ ถ้า a = 5 แล้ว a + 3 = 5 + 3 สมบตั ิของการเท่ากันเก่ียวกับการคูณ ถา้ a = b แลว้ ca = cb เม่อื a, b และ c แทนจำนวนใดๆ (multiplicative property of equality) เช่น ถ้า n = 2 แล้ว 3n = 6 จงเตมิ ข้อความตอ่ ไปนใ้ี ห้สมบูรณ์ 1. ให้ m + 1 = 1 และ 1 = n ดังนั้น ...................... = n โดยใช้สมบัติ ......................................................... 33 2. ให้ y = 3(2x + 5) และ 3(2x + 5) = 14 ดังน้นั y = ………… โดยใชส้ มบตั ิ ................................................... 3. ให้ p = 9 ดังน้ัน p – 4.5 = ………………………. โดยใช้สมบัติ ......................................................................... 4. ให้ x – 7 = 15 ดงั นนั้ (x - 7) + 7 = …………………………. โดยใชส้ มบัติ ........................................................ 5. ให้ 11x + 9 = 41 ดังนั้น .......................... = 32 โดยใช้สมบัติ ...................................................................... 6. ให้ t2 = 165 ดงั นน้ั 165 = ……………….. โดยใชส้ มบัติ ................................................................................. 7. ให้ 1 w = 10 ดงั นั้น .......................... = 20 โดยใช้สมบัติ ........................................................................... 2 8. ให้ − m = n ดงั นน้ั n = .......................... โดยใช้สมบัติ .............................................................................. 13 9. ให้ − 4x − 1 = 1 ดังนั้น -4x = .......................... โดยใช้สมบัติ ................................................................... 22 10. ให้ 16 = 16y ดงั นัน้ .................. = y โดยใช้สมบัติ ..................................................................................... แบบฝึกหัด 1.3 ข การแกส้ มการเชิงเสน้ ตัวแปรเดียว

7 จงแกส้ มการตอ่ ไปนี้ 1. a – 10 = -5 2. 2.6 = b – 0.2 วิธีทำ ........................................................................ วธิ ีทำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 3. c – (-1) = 13 4. d - 1 = 1 วิธที ำ ........................................................................ 42 .................................................................................. วธิ ที ำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. ................................................................................... .................................................................................. ................................................................................... .................................................................................. 5. e + 5 = 19 6. -4 = f + 3.5 วิธที ำ ........................................................................ วิธีทำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 7. h + 1 = 2 8. j + 4 = − 2 33 5 10 วธิ ที ำ ........................................................................ วธิ ที ำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. ..................................................................................

8 9. p = 5 10. q = 4 3 −4 วิธีทำ ........................................................................ วธิ ีทำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. ……………………………………………………………………….. 11. −10 = m 12. − 5 = n 8 −2 วธิ ีทำ ........................................................................ วิธที ำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. ................................................................................... .................................................................................. ................................................................................... .................................................................................. 13. 9x = 72 14. -2y = 100 วธิ ที ำ ........................................................................ วิธที ำ ........................................................................ 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.................................................................................. .................................................................................. .................................................................................. .................................................................................. 15. -2.5 = 0.5w 16. -24 = -3z วธิ ีทำ ........................................................................ วิธที ำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 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9 แบบฝกึ หดั 1.3 ค การแกส้ มการเชิงเสน้ ตวั แปรเดยี ว 1. จงแกส้ มการต่อไปนี้ 1. 5x + 6 = 31 2. 3y + 4 = -17 วธิ ที ำ ........................................................................ วธิ ีทำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 3. -112 – 2x = -24 4. -0.3y – 0.6 = 0.9 วธิ ที ำ ........................................................................ วิธที ำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. ................................................................................... .................................................................................. ................................................................................... .................................................................................. .................................................................................. .................................................................................. .................................................................................. 5. 12(9 - x) = 84 6. 0.6(y + 0.5) = 0.15 วิธีทำ ........................................................................ วิธีทำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. ..................................................................................

10 7. 1 (y − 4) = 7 8. x +1 = 7 35 วิธที ำ ........................................................................ วิธที ำ ........................................................................ .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 9. 7x – 2 = 8 + 2x 10. 6(x + 1) = 3x วิธที ำ ........................................................................ วิธที ำ ........................................................................ 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................................................................................... .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. .................................................................................. 11. 16 y = 4 + 1 y 12. x − 8 = x + 1 55 23 53 วิธีทำ ........................................................................ วิธที ำ ........................................................................ .................................................................................. 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11 แบบฝกึ หดั 1.4 ก โจทย์ปญั หาเกยี่ วกบั สมการเชิงเสน้ ตัวแปรเดยี ว จงเขียนสมการจากปัญหาในแต่ละขอ้ ต่อไปน้ี เม่ือ x แทนจำนวนท่ตี อ้ งการหา 1. เศษหนึง่ ส่วนสข่ี องจำนวนจำนวนหน่งึ เท่ากบั 15 จงหาจำนวนนน้ั ตอบ ............................................................................................. 2. แปดเท่าของจำนวนจำนวนหนง่ึ มากกว่า 3 อยู่ 96 จงหาจำนวนนัน้ ตอบ ............................................................................................. 3. แปดเท่าของสว่ นที่จำนวนจำนวนหนงึ่ มากกวา่ 3 อยู่ 96 จงหาจำนวนน้ัน ตอบ ............................................................................................. 4. เศษสองสว่ นสามของจำนวนจำนวนหนงึ่ น้อยกวา่ 45 อยู่ 13 จงหาจำนวนนน้ั ตอบ ............................................................................................. 5. เอดสิ ันเกดิ เมอ่ื ค.ศ. 1847 เขาประดิษฐ์หลอดไฟฟา้ สำเรจ็ เมอื่ ค.ศ. 1879 จงหาอายุในปีทเ่ี ขา ประดษิ ฐ์หลอดไฟฟ้าสำเรจ็ ตอบ ............................................................................................. 6. ในการแขง่ ขันกีฬาบาสเกต็ บอลของโรงเรียนนำชยั วทิ ยา กระดานคะแนนดจิ ทิ ัลทใ่ี ช้บอกคะแนนเสยี ทำให้ไมป่ รากฎคะแนนของทีม B แต่ทราบว่าทีม B มีคะแนนนำทีม A อยู่ 13 คะแนน ถา้ ทมี A มีคะแนน 46 คะแนน ทมี B จะมีคะแนนเท่าใด ตอบ ............................................................................................. 7. ถ้าไมค่ ิดกระดกู ส่วนหวั 29 ชน้ิ แล้วร่างกายมนษุ ยจ์ ะมกี ระดูกของส่วนทเี่ หลือ 177 ช้นิ จงหาว่าในรา่ งกายมนุษย์มกี ระดกู ทั้งหมดกช่ี ิ้น ตอบ ............................................................................................. 8. อกี สามปี มานะจะมอี ายุครบ 21 ปี จงหาอายุปจั จุบันของมานะ ตอบ ............................................................................................. 9. ต้นน้ำหยอดเงินในกระปกุ ออมสินวนั ละเท่า ๆ กนั เมอื่ เวลาผ่านไปหน่ึงเดอื น ตน้ นำ้ มีเงนิ ในกระปกุ ออมสนิ 600 บาท ต้นนำ้ ออมเงนิ วันละก่ีบาท (กำหนดให้ 1 เดอื น มี 30 วัน) ตอบ ............................................................................................. 10. น้อยมเี งินมากกว่านิด 6 บาท ทัง้ สองคนมเี งนิ รวมกัน 40 บาท จงหาจำนวนเงนิ ของน้อย ตอบ ............................................................................................. 11. เมอื่ ห้าปที ่ีแลว้ ฝาแฝดสองคนมีอายรุ วมกันเปน็ 18 ปี จงหาวา่ อายุปัจจุบันฝาแฝดคนู่ มี้ อี ายุเท่าใด ตอบ .............................................................................................

12 แบบฝึกหดั 1.4 ข โจทยป์ ญั หาเก่ยี วกับสมการเชงิ เสน้ ตัวแปรเดยี ว จงแก้ปัญหาตอ่ ไปนี้ 1. เศษสามส่วนห้าของจำนวนจำนวนหนึง่ มากกวา่ 15 อยู่ 60 จงหาจำนวนนัน้ .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. 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.............................................................................................................................................................................. 2. ห้าเท่าของจำนวนจำนวนหนึง่ รวมกบั 1 ของจำนวนนนั้ แล้วได้ผลลพั ธเ์ ปน็ 390 จงหาจำนวนนัน้ 5 .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. 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.............................................................................................................................................................................. 3. ถ้านำ 6 มาบวกกับจำนวนจำนวนหน่ึง แลว้ สเี่ ท่าของผลบวกนน้ั คอื 48 จงหาจำนวนนนั้ .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. 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13 4. สามในห้าของจำนวนจำนวนหนง่ึ นอ้ ยกวา่ สองในสามของจำนวนนั้นอยู่ 23 จงหาจำนวนน้ัน .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. 5. จงหาจำนวนคีส่ ามจำนวนทเี่ รียงตดิ กนั จากน้อยไปมาก มีผลบวกของสองจำนวนแรกเปน็ สามเท่าของจำนวน ท่ีสามแลว้ จงหาจำนวนเต็มสามจำนวนนน้ั .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. 6. ถา้ ผลบวกของจำนวนเตม็ สองจำนวนเทา่ กับ 20 และผลต่างของจำนวนสองจำนวนนนั้ เทา่ กับ 2 จงหาจำนวนสองจำนวนนน้ั 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14 7. 2 ของจำนวนนกั เรียนในห้องหนงึ่ เปน็ นกั เรยี นหญิง ถ้ามีนกั เรยี นหญงิ ในห้อง 18 คน 3 นกั เรยี นในหอ้ งนีม้ ีก่ีคน .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. 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.............................................................................................................................................................................. 8. ตอ่ และตอ้ สะสมเงนิ ไวซ้ ื้อของขวญั วนั เกดิ ให้คุณแม่ หลงั จากนำเงนิ ทแี่ ต่ละคนสะสมไว้มารวมกันไปซ้อื ของขวัญให้คุณแมเ่ ปน็ เงนิ 620 บาท แล้วปรากฎวา่ ยงั เหลือเงนิ อยอู่ กี 135 บาท ถ้าต่อสะสมเงนิ ได้ 440 บาท จงหาว่าตอ้ สะสมเงินไดเ้ ทา่ ไร .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. 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15 9. จงหาความยาวของดา้ นประกอบมุมยอดของรูปสามเหลย่ี มหนา้ จ่วั ซึ่งมีเสน้ รอบรปู ยาว 33 เซนติเมตร และฐานยาย 9 เซนติเมตร .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. 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.............................................................................................................................................................................. 10. จงหาความยาวของด้านกว้างและด้านยาวของรูปสี่เหลย่ี มมุมฉากรปู หนึ่งท่มี ีด้านยาว ยาวเป็นสามเท่า ของดา้ นกวา้ ง และมีเสน้ รอบรปู ยาว 48 เซนติเมตร .............................................................................................................................................................................. .............................................................................................................................................................................. .............................................................................................................................................................................. 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