When you do a difficult calculation, it is often a good idea to check your
One way to do this is to re-do the calculation in reverse.
This is called doing the inverse.
+ is the opposite to -
x is the opposite to ÷
If you think 52 ÷ 4 = 13
You could check by doing 13 x 4 to see if you get back to 52.
If you think 63 - 24 = 39
You could check by doing 39 + 24 to see if you get back to 63.