Doubles

A double is two groups that are exactly the same size.

Double means adding a number to itself, like 6 + 6.

Why doubles are worth knowing

Doubles are easy to picture, so they are easy to remember. Once you know them, they help you with everything else.

Every double gives an even answer. Two equal groups always share out evenly.

Why doubles are worth memorising

A double is an addition fact where both numbers are the same: 4 + 4, 7 + 7, 9 + 9. There are only ten of them to learn, and once they are in your head they come back instantly, without counting. That speed is the whole point. Every other fact you meet can be reached from a double in one small step, so ten memorised facts do the work of far more.

Doubles you can already see

Your hands are 5 + 5. A pair of shoes is 1 + 1. An egg box holds 6 + 6. A week is 7 + 7 for two weeks. A month has about 15 + 15 days. When you meet a double you cannot recall, look for the thing in the world that shows it — the picture is easier to remember than the numbers.

Checking a double

Every double gives an even answer. Always. If you work out 6 + 6 and get 13, you can stop and try again before anyone tells you, because 13 is odd and a double can never be odd. This is your first taste of checking an answer using a rule rather than by redoing the work.