How can compensating make adding and subtracting easier?

Part ofMaths and NumeracyNumbers and number processes

Snoot and Fin use compensation to make adding and subtracting two digit numbers easier.

What is compensating?

Everyone finds some numbers easier to work with than others. You might find adding or taking away 10 is easier than 9 or 11.

Compensation is a way of adding or taking away numbers that you find easier.

You add or take away a bit too much or a bit too little, so then you have to add or take away this too.

Example

26 - 9 = ?

Try taking away 10 instead.

26 - 10 = 16

You have taken away 1 too many (10 is 1 more than 9)

So add the 1 back on

16 + 1 = 17

It works for adding too

33 + 12 = ?

Try adding 10 instead.

33 + 10 = 43

You need to add on 2 more (10 is 2 less than 12)

43 + 2 = 45

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Quiz

Fin and Snoot add up some of their favourite snacks: space grubs and astro bugs.

Which way round should I add two numbers?

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