b) 33 to 42 33 ___ ___ ___ ___ ___ ___ ___ ___ 42 c) 26 to 45 26 ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ 45 ___ ___ ___ ___ ___ ___ ___ d) 21 to 25 21 ___ ___ ___ 25 & Remembering and Understanding To add two numbers mentally, first keep the bigger number in mind. Then, count the smaller one on the fingers. If the two given numbers are the same, we can keep any number in mind and count the other number on the fingers. Addition 47 NR_BGM_9789388751797 ALPINE G01 MATHS TEXTBOOK PART 1_Text.pdf 51 12/24/2018 2:37:21 PM
Let us understand, through these examples. Example 10: Add 2 and 5 mentally Solution: Follow these steps to add mentally: Steps Solved Solve this 2+5 3+6 Step 1: Keep the bigger number in mind. The bigger number is 5. The bigger number is So, keep 5 in mind. ____. So, keep ____ in Step 2: Keep as many The smaller number is mind. fingers open as the 2. So, keep 2 fingers The smaller number is smaller number. open. ____. So, keep ____ fingers Step 3: Begin counting The number after 5 is open. the fingers. Start from the 6. Count 2 fingers as 6 The number after ____ is number after the bigger and 7. number. ____. Count ____ fingers as ____ ,_____ and _____. Step 4: Write the last The sum of 2 and 5 is 7. The sum of 3 and 6 is ___. number as the sum of the given numbers. Example 11: Add 6 and 7 mentally Solution: Follow the steps to add mentally: Steps Solved Solve this Step 1: Keep the bigger 6+7 5+9 number in your mind. The bigger number is 7. The bigger number is So, keep 7 in mind. ____. So, keep ____ in mind. Step 2: Keep as many The smaller number is The smaller number is fingers open as the 6. So, keep 6 fingers ____. So, keep ___ fingers smaller number. open. open. 48 12/24/2018 2:37:21 PM NR_BGM_9789388751797 ALPINE G01 MATHS TEXTBOOK PART 1_Text.pdf 52
Steps Solved Solve this 6+7 5+9 Step 3: Begin counting the fingers. Start from the The number after 7 is 8. The number after _____ is number after the bigger Count 6 fingers as 8, 9, number. ____. Count ____ fingers 10, 11, 12 and 13. as ____, ____, ____, ____ and ____. Step 4: Write the last The sum of 6 and 7 The sum of 5 and 9 is _________. number as the sum of the is 13. given numbers. Application We have seen how easy it is to add two 1-digit numbers mentally. Let us now see a few real life-examples. Example 12: In a class, Team A has 5 students and Team B has 7 students. How many students are there in all? Solution: Number of students in Team A = 5 Number of students in Team B = 7 The bigger number is 7. Keep 7 in the mind. The smaller number is 5. Keep 5 fingers open. After 7, count 5 fingers as 8, 9, 10, 11 and 12. So, the total number of students in the class is 12. Example 13: Seema has 3 milk chocolates and 6 dark chocolates. How many chocolates does she have in all? Solution: Number of milk chocolates = 3 Number of dark chocolates = 6 The bigger number is 6. Keep 6 in the mind. The smaller number is 3. Keep 3 fingers open. After 6, count 3 fingers as 7, 8 and 9. So, Seema has 9 chocolates in all. Addition 49 NR_BGM_9789388751797 ALPINE G01 MATHS TEXTBOOK PART 1_Text.pdf 53 12/24/2018 2:37:22 PM
Higher Order Thinking Skills (H.O.T.S.) We have seen mental addition of two 1-digit numbers. Let us now add three 1-digit numbers mentally. Example 14: Add mentally: 3, 5 and 7 Solution: Follow the steps to add mentally: Steps Solved Solve this 3, 5 and 7 4, 6 and 8 Step 1: Choose the first two numbers. The first two numbers The first two numbers are are 3 and 5. ____ and ____. Step 2: Keep the bigger The bigger number is 5. The bigger number is number in mind. So, keep 5 in mind. ____. So, keep ____ in mind. Step 3: Keep as many The smaller number is The smaller number fingers open as the 3. So, keep 3 fingers is _____. So, keep _____ smaller number of the 2 open. fingers open. numbers. Step 4: Begin counting The number after _____ is the fingers. Count from the number after the The number after 5 is 6. _____. Count the ______ bigger number. Count the 3 fingers as fingers as _____ , _____ , 6, 7 and 8. _____ and ______. Step 5: Compare the sum The sum of the first two of the first two numbers The sum of the first two with the third number. numbers is 8. So, keep numbers is _____. So, Keep the bigger number 8 in mind. keep _____ in mind. in mind. 50 12/24/2018 2:37:22 PM NR_BGM_9789388751797 ALPINE G01 MATHS TEXTBOOK PART 1_Text.pdf 54
Steps Solved Solve this 3, 5 and 7 4, 6 and 8 Step 6: Keep as many The third number is The third number is ____. fingers open as the third 7. So, keep 7 fingers So, keep ______ fingers number. open. open. Step 7: Begin counting The number after ______ the fingers. Count from the number after the is _____. Count the sum of the first two The number after 8 is 9. numbers. Count the 7 fingers as ______ fingers as _____ 9, 10, 11, 12, 13, 14 and , _____ , _____ , _____ , Step 8: Write the last 15. number as the sum. _____ , _____ , _____ , and _____. The sum of 3, 5 and 7 The sum of 4, 6 and 8 is is 15. _____. Example 15: R ahul has 3 apples, 4 chikoos and 6 bananas in his basket. How many fruits does he have in all? Solution: Number of apples in the basket = 3 Number of chikoos in the basket = 4 Number of bananas in the basket = 6 So, the first two are 3 apples and 4 chikoos. The bigger number is 4. Keep 4 in the mind. The smaller number is 3. Open 3 fingers. After 4, count 3 fingers as 5, 6 and 7. So, the sum of the first two numbers is 7. The number of bananas is 6. The bigger number is 7. Keep 7 in the mind. The smaller number is 6. Open 6 fingers. After 7, count 6 fingers as 8, 9, 10, 11, 12 and 13. So, Rahul has 13 fruits in all. Addition 51 NR_BGM_9789388751797 ALPINE G01 MATHS TEXTBOOK PART 1_Text.pdf 55 12/24/2018 2:37:22 PM
Drill Time Concept 4.1: Add 1-digit and 2-digit Numbers 1) Add the following numbers using the Number line. a) 3 and 3 b) 2 and 6 c) 1 and 7 d) 4 and 2 e) 3 and 4 2) Add the following numbers using the vertical or column method. a) 2 and 5 b) 3 and 6 c) 21 and 42 d) 17 and 61 e) 10 and 40 3) Word problems a) I have 2 pens and my sister has 2 pens. What is the total number of pens with us? b) Krish picked 12 sticks and Sanjay picked 20 sticks. How many sticks did they pick in all? Concept 4.2: Add Two 1-digit Numbers Mentally 4) Add mentally a) 2 and 7 b) 1 and 3 c) 3 and 3 d) 8 and 2 e) 7 and 9 52 12/24/2018 2:37:22 PM NR_BGM_9789388751797 ALPINE G01 MATHS TEXTBOOK PART 1_Text.pdf 56
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