← Methods
Round & Adjust
Taking away 40 is easy; taking away 38 is not. Take the round number off, then hand back the two you overpaid.
When it works
The number you are taking away ends in 6, 7, 8 or 9.
Worked through
72 − 38 = 34
- 72 − 40 = 32Round 38 up to 40. A round number is easier to take away.
- 32 + 2 = 34You took 2 too many, so give them back.
10 problems, every one of them this method.