Addition & subtraction
Number Bonds to 20
Year 1 · Year 2
- ✓By the end of this lesson students will be able to understand what number bonds are.
- ✓By the end of this lesson students will be able to recall number bonds to 10.
- ✓By the end of this lesson students will be able to recall number bonds to 20.
- ✓By the end of this lesson students will be able to understand and use fact families related to number bonds.
- ✓By the end of this lesson students will be able to apply number bonds to solve simple addition and subtraction problems.
Key concepts
Number bonds are pairs of numbers that add together to make a specific total. They help us to quickly know which numbers 'go together' to make a sum. For example, 3 and 7 are a number bond to 10 because 3 + 7 = 10.
These are pairs of numbers that add up to 10. Knowing these helps you do maths quickly in your head. Examples include: 1 + 9 = 10, 2 + 8 = 10, 5 + 5 = 10, and 0 + 10 = 10.
These are pairs of numbers that add up to 20. They are similar to bonds to 10 but with larger numbers. Examples include: 1 + 19 = 20, 10 + 10 = 20, 15 + 5 = 20, and 0 + 20 = 20.
A fact family shows how addition and subtraction are related using the same three numbers. If you know one number bond, you can make four different maths sentences (two addition and two subtraction). For example, if 3 + 7 = 10, then 7 + 3 = 10, 10 - 3 = 7, and 10 - 7 = 3 are all part of the same fact family.
Key facts to remember
- 1Number bonds are pairs of numbers that add up to a specific total.
- 2Knowing your number bonds helps you do addition and subtraction quickly.
- 3The order of numbers in addition does not change the total (e.g., 3 + 7 is the same as 7 + 3).
- 4Every addition sentence has two related subtraction sentences.
- 5Examples of bonds to 10: 1+9, 2+8, 3+7, 4+6, 5+5, 0+10.
- 6Examples of bonds to 20: 1+19, 5+15, 10+10, 12+8, 17+3, 0+20.
- 7A fact family links two addition and two subtraction sentences using the same three numbers.
Worked examples
Example 1
What number goes with 6 to make a bond to 10?
Answer
4
You can use your fingers or objects to help you count.
Example 2
Find the missing number: 12 + ___ = 20.
Answer
8
Knowing your bonds to 10 can help here. 2 + 8 = 10, so 12 + 8 = 20.
Example 3
Write the fact family for the number bond 4 + 6 = 10.
Answer
4 + 6 = 10 6 + 4 = 10 10 - 4 = 6 10 - 6 = 4
A fact family always has two addition and two subtraction sentences (unless the numbers are the same, like 5+5=10).
Common mistakes
- ✗Forgetting that 0 is a number and can be part of a number bond (e.g., 0 + 10 = 10).
- ✗Confusing bonds to 10 with bonds to 20, or vice versa.
- ✗Only writing one addition and one subtraction for a fact family, instead of two of each.
- ✗Not understanding that subtraction is the inverse (opposite) of addition.
- ✗Counting on fingers for every problem instead of trying to recall the bonds from memory.
Exam tips
- ★Practise your number bonds every day, perhaps with flashcards or online games.
- ★Look for patterns! For example, if you know 1+9=10, then 10+9=19 (or 1+19=20).
- ★Use objects like counters or blocks to help you visualise the numbers when you are learning.
- ★Always check your answers by doing the sum again, or by using the inverse operation (e.g., if you added, check with subtraction).
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