Numbers

2-22 Checking Add. & Sub.

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You can use addition to check subtraction because addition is the opposite of subtraction. You can use subtraction to check addition because subtraction is the opposite of addition.

For example: 15 - 8 = 7 or 8 + 7 = 15.

 

Use the opposite to check each problem below.

18 - 9 = 9

9 + 9 =

17 - 9 = 8

9 + 8 =

15 - 9 = 6

9 + 6 =

     
9 + 7 = 16

16 - 7 =

8 + 4 = 12

12 - 4 =

6 + 9 = 15

15 - 9 =

     
15 - 7 = 8

8 + 7 =

13 - 6 = 7

7 + 6 =

19 - 8 = 11

11 + 8 =

     
9 + 9 = 18

18 - 9 =

8 + 8 = 16

16 - 8 =

7 + 7 = 14

14 - 7 =

 
 

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