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Doubles and halves

You learn your doubles by heart, and how to use them for near doubles and halves.

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How to work it out

  1. Learn doubles by heart: 6 + 6 = 12.
  2. If one number is 1 more, double and add 1.
  3. For halving, find which double gives that number.

A worked example

7 + 7

  1. This is a double.
  2. Double 7 is 14.
  3. So 7 + 7 = 14.
More examples

6 + 7

  1. Use the double: 6 + 6 = 12.
  2. Add one more: 12 + 1 = 13.
  3. So 6 + 7 = 13.

16 − 8

  1. Find the double that makes 16: 8 + 8 = 16.
  2. Half of 16 is 8.
  3. So 16 − 8 = 8.

7 + 8

  1. The smaller number is 7.
  2. Use the double: 7 + 7 = 14.
  3. Add one more: 14 + 1 = 15.
  4. So 7 + 8 = 15.

Try it yourself

  1. 2 + 2 =

  2. 14 − 7 =

Watch out

  • For 6 + 7 you add one too few or one too many and say 12 or 14.

    Double the smaller number, then add exactly one more.

Tips

  • Is the second number one less, like 6 + 5? Double 6 and take one away.
  • Halving is doubling the other way round: half of 14 is 7.

Why it works

Doubles are easy to remember: two hands, two feet, two rows of eggs in a box. If you know 6 + 6 = 12, you know 6 + 7 straight away: it is one more. And halving is doubling the other way round: half of 12 is 6.