Partitioning to ten
You learn how many more you need to get from a small number to a bigger one.
How to work it out
- Start at the number you have.
- Count on to the target number.
- The count is the missing part.
A worked example
3 + _ = 8
- Start at 3.
- Count on to 8: 4, 5, 6, 7, 8.
- You said 5 numbers, so 3 + 5 = 8.
More examples
4 + _ = 7
- Start at 4.
- Count on to 7: 5, 6, 7.
- You said 3 numbers, so 4 + 3 = 7.
2 + _ = 9
- Start at 2.
- Count on to 9: 3, 4, 5, 6, 7, 8, 9.
- You said 7 numbers, so 2 + 7 = 9.
5 + _ = 9
- Start at 5.
- Count on to 9: 6, 7, 8, 9.
- You said 4 numbers, so 5 + 4 = 9.
Try it yourself
3 + • = 9
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.