Numbers to 20 · Usually met around P1
Number bonds to 20
Look at the ones: reuse the pairs to 10.
How to do it
Method
Look at the ones: reuse the pairs to 10
17 + 3 = 20 (7 + 3 = 10)
Another way
Subtraction
20 − 17 = 3
In full
Reuse your pairs to ten. For 17 + ? = 20, look at the ones digit, 7. Its partner is 3. With a single digit, 3 + ? = 20: 3 pairs with 7, plus a ten → 17. Bonds to twenty are just bonds to ten with a ten in front.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
18 + ? = 20
Show the answer and working
Answer: 18 + 2 = 20
Look at the ones: 8 goes with 2 to make ten, 18 + 2 = 20
Example 2
6 + ? = 20
Show the answer and working
Answer: 6 + 14 = 20
6 goes with 4 to make ten, and one more ten: 4 + 10 = 14, 6 + 14 = 20
Example 3
8 + ? = 20
Show the answer and working
Answer: 8 + 12 = 20
8 goes with 2 to make ten, and one more ten: 2 + 10 = 12, 8 + 12 = 20
Practise it in the game →Numbers to 20 · Free to start, unlimited questions, no download