Add by rounding, then adjust

Round the awkward number up, add easily, then give back the difference.

The question

What is 47 + 38?

The trick

Round one number to the nearest ten, do the easy addition, then subtract however much you rounded up by.

Worked example

1Round 38 up to 40 — that is 2 extra
247 + 40 = 87
3Give back the 2: 87 − 2 = 85

So: 85

Remember it like this

Borrow a little to make it round, then pay it straight back.

In the exam

This shines when a number is just under a round figure, like 99 or 998. 245 + 99 → 245 + 100 − 1 = 344. Spotting the near-round number is the whole skill.

Why it works

You are adding and then removing the same amount, so the total never changes — but the middle step becomes something you can do without writing anything down.

Explain this to my childGet the words to teach it, in your language

Try it yourself

0/4 correct

1
56 + 29
56 + 29
2
78 + 96
78 + 96
3
245 + 99
245 + 99
4
63 + 48
63 + 48