Number bonds to 20
Every pair of numbers that makes 20, and the shortcut: each one is a bond to 10 with an extra 10 on one side.
The answer
The number bonds to 20 are 0 + 20, 1 + 19, 2 + 18, 3 + 17, 4 + 16, 5 + 15, 6 + 14, 7 + 13, 8 + 12, 9 + 11 and 10 + 10, and the same pairs turned round.
Every number bond to 20
| Bond | On a twenty frame |
|---|---|
| 0 + 20 = 20 | |
| 1 + 19 = 20 | |
| 2 + 18 = 20 | |
| 3 + 17 = 20 | |
| 4 + 16 = 20 | |
| 5 + 15 = 20 | |
| 6 + 14 = 20 | |
| 7 + 13 = 20 | |
| 8 + 12 = 20 | |
| 9 + 11 = 20 | |
| 10 + 10 = 20 | |
| 11 + 9 = 20 | |
| 12 + 8 = 20 | |
| 13 + 7 = 20 | |
| 14 + 6 = 20 | |
| 15 + 5 = 20 | |
| 16 + 4 = 20 | |
| 17 + 3 = 20 | |
| 18 + 2 = 20 | |
| 19 + 1 = 20 | |
| 20 + 0 = 20 |
Try it on a twenty frame
3 + 17 = 20
Each time one part goes up, the other goes down by the same amount, so the total stays 20.
The pattern
Every bond to 20 is a bond to 10 with an extra 10 on one side. 3 + 7 = 10, so 13 + 7 = 20 and 3 + 17 = 20. Even 10 + 10 fits: it is 0 + 10 with the extra 10 on the 0.
On the twenty frame the top row is one ten and the bottom row is the other. If a child can see how many are missing from one row, they can see the bond.
Using the bonds
A bond with two different numbers gives four facts. Knowing 6 + 14 = 20 also gives 14 + 6 = 20, 20 − 6 = 14 and 20 − 14 = 6. A double such as 10 + 10 gives only two: 10 + 10 = 20 and 20 − 10 = 10.
They help with subtracting across ten too. For 20 − 6, the bond 6 + 14 = 20 gives the answer, 14, straight away. Year 2 children are expected to recall facts to 20 fluently.
More number bonds and mental maths
Questions parents ask
What goes with 8 to make 20?
12. 8 + 2 makes 10, and one more 10 makes 20, so 8 + 12 = 20.
What is 20 take away 7?
13, because 7 + 13 = 20. It comes from the bond 7 + 3 = 10, with an extra 10 on the 3.
How many number bonds to 20 are there?
There are 21 if you count every order, from 0 + 20 up to 20 + 0. If 6 + 14 and 14 + 6 count as the same bond, there are 11.
When should children know number bonds to 20?
By the end of Year 2. The national curriculum asks Year 2 children to recall and use addition and subtraction facts to 20 fluently.
Quick mental maths starts with number bonds
11+ maths is timed, and number bonds are behind fast adding, subtracting and working out change. The free diagnostic checks maths, English and both kinds of reasoning, and shows what to practise next. No card is required.