Number bonds to 10 and 20

Number bonds are pairs of numbers that add up to a total, like 7 + 3 = 10. Knowing the bonds to 10 by heart makes adding and taking away much quicker.

Key facts

  • Bonds to 10: 0 + 10, 1 + 9, 2 + 8, 3 + 7, 4 + 6, 5 + 5.
  • If you know 3 + 7 = 10, you also know 7 + 3 = 10, 10 − 7 = 3 and 10 − 3 = 7.
  • Bonds to 20 come from bonds to 10: 3 + 7 = 10, so 13 + 7 = 20.
  • Bonds to 100 use tens: 30 + 70 = 100.

Worked examples

Example 1

A ten frame has 6 dots. How many more fill it?

  1. There are 10 squares and 6 are full.
  2. Count the empty squares: 4.

Answer: 4

Example 2

Use 4 + 6 = 10 to work out 14 + 6.

  1. 4 + 6 = 10
  2. 14 is 10 more than 4, so the answer is 10 more than 10. 14 + 6 = 20

Answer: 20