Inverse operations with tens
Addition and subtraction undo each other: if 30 + 40 = 70, then 70 − 40 = 30 and 70 − 30 = 40. Second graders write the related (inverse) fact for tens problems and use it to check their answers.
How to solve this
- An inverse task with tens uses the opposite operation: if 40 + 30 = 70, then 70 − 30 = 40 and 70 − 40 = 30.
- Write the related fact family: one addition and two subtractions all use the same three numbers.
- Check that all three equations in the family give the correct result before moving on.
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.
- 40 + 50 = 90 → 90 − 40 = ___
- 100 − 30 = 70 → 30 + 70 = ___
- 100 − 60 = 40 → 60 + 40 = ___
- 80 + 10 = 90 → 90 − 10 = ___
- 60 − 20 = 40 → 20 + 40 = ___
- 70 − 30 = 40 → 30 + 40 = ___
- 80 + 20 = 100 → 100 − 20 = ___
- 70 + 30 = 100 → 100 − 70 = ___
Show answers
- 50
- 100
- 100
- 80
- 60
- 70
- 80
- 30