Every plus problem has a matching minus problem, and the other way round!
From plus to minus:
35 + 20 = 55 → 55 − 20 = 35
From minus to plus:
60 − 18 = 42 → 42 + 18 = 60
Always write the matching inverse problem next to it.
The numbers filled in show the solution.
Example
For parents
What does this exercise practice?
This exercise shows that plus and minus are inverse operations. Whoever understands this can check their work and find mistakes on their own.
Common pitfalls
Children often just flip the operation signs but mix up the positions of the numbers. Saying it out loud helps: 55 minus 20 is 35, so 35 plus 20 is 55.
How to practice at home
With building blocks: lay out 50 blocks, take away 20, count. Then put them back: how many do we need to add to have 50 again? Doing it physically makes the reversal visible.
Related: Calculation, Swap