**Compensation in addition and subtraction? **

You can often convert an addition or subtraction question into an easier question by temporarily adding or subtracting an appropriate small number. For example, many people would evaluate 673 + 99 by adding 1 temporarily to the 99, so the question becomes 673 + 100. This gives 773. Now take off the extra 1, to get the answer 772. This strategy is sometimes called *compensation.*

The trick in the strategy is always to be on the lookout for an easier calculation than the one that you have to do. This will often involve temporarily replacing a number ending in a 9 or an 8 with the next multiple of 10.

For example, the subtraction, 83 – 28, can temporarily be changed into the much easier calculation, 83 – 30, which gives 53, with 2 to be added to this to compensate for the fact that we’ve actually taken away 2 more than required.