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Partitioning to ten

You learn how many more you need to get from a small number to a bigger one.

Practise thisWhiteboardMake it a quiz

How to work it out

  1. Start at the number you have.
  2. Count on to the target number.
  3. The count is the missing part.

A worked example

3 + _ = 8

  1. Start at 3.
  2. Count on to 8: 4, 5, 6, 7, 8.
  3. You said 5 numbers, so 3 + 5 = 8.
More examples

4 + _ = 7

  1. Start at 4.
  2. Count on to 7: 5, 6, 7.
  3. You said 3 numbers, so 4 + 3 = 7.

2 + _ = 9

  1. Start at 2.
  2. Count on to 9: 3, 4, 5, 6, 7, 8, 9.
  3. You said 7 numbers, so 2 + 7 = 9.

5 + _ = 9

  1. Start at 5.
  2. Count on to 9: 6, 7, 8, 9.
  3. You said 4 numbers, so 5 + 4 = 9.

Try it yourself

  1. 3 + • = 9

  2. 4 + • = 9

Watch out

  • You count the number you start at as well: for 3 + _ = 8 you count 3, 4, 5, 6, 7, 8 and get 6.

    Start counting at the number after 3. You already have the 3.

Tips

  • Use your fingers: put up one finger for each number you say.
  • Check with an addition: 3 + 5 = 8, so it is right.

Why it works

You can split a number in lots of ways: 8 is 3 and 5, but also 6 and 2. If you count on from the small part, you always find the other part. The more you practise, the faster you just know the pair.