Stage 1 · Number sense
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 the ten pairs: for 17 + ? = 20 look at the ones digit 7, whose partner is 3. With a single digit, 3 + ? = 20: 3 pairs with 7, plus a ten → 17. Bonds to twenty are 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
5 + ? = 20
Show the answer and working
Answer: 5 + 15 = 20
5 goes with 5 to make ten, and one more ten: 5 + 10 = 15, 5 + 15 = 20
Example 3
4 + ? = 20
Show the answer and working
Answer: 4 + 16 = 20
4 goes with 6 to make ten, and one more ten: 6 + 10 = 16, 4 + 16 = 20
Example 4
9 + ? = 20
Show the answer and working
Answer: 9 + 11 = 20
9 goes with 1 to make ten, and one more ten: 1 + 10 = 11, 9 + 11 = 20
Practise bonds to 20 in the game →Stage 1 · Number sense · Free to start, unlimited questions, no download