Inverse operations
Three numbers such as 28, 9 and 37 make a fact family: two addition facts and two subtraction facts. Knowing that subtraction undoes addition lets second graders check every answer, for example 37 − 9 = 28 because 28 + 9 = 37.
How to solve this
- Every addition has two related subtraction facts, and every subtraction has a related addition fact.
- Write all related facts as a family: for 36 + 48 = 84, also write 84 − 48 = 36 and 84 − 36 = 48.
- Check that all equations in the family use the same three numbers and that every one is correct.
Examples
30 + 40 = 70
70 - 40 = 30
28 + 9 = 37
37 - 9 = 28
Practice problems with answers
Solve these problems on paper or out loud, then check the answer key. The online practice and the printable worksheet give a new set every time.
- 46 + 10 = 56 → 56 − 46 = ___
- 60 + 34 = 94 → 94 − 60 = ___
- 7 + 4 = 11 → 11 − 4 = ___
- 68 − 58 = 10 → 58 + 10 = ___
- 71 − 58 = 13 → 58 + 13 = ___
- 34 + 3 = 37 → 37 − 34 = ___
- 51 + 37 = 88 → 88 − 37 = ___
- 68 − 46 = 22 → 46 + 22 = ___
Show answers
- 10
- 34
- 7
- 68
- 71
- 3
- 51
- 68