Year 1: Number bonds to 20
Part of the Year 1 adding and subtracting within 20 chapter. Chapter overview · whole chapter on one page · Download worksheet (PDF) · Answers (PDF)
Number bonds to 20
A number bond is two numbers that make a total. The total is the whole. The two numbers are the parts.
Look at this picture. The whole is 14. One part is 9 and the other part is 5. Nine and five make fourteen.
One picture gives you four facts: 9 + 5 = 14, 5 + 9 = 14, 14 − 5 = 9 and 14 − 9 = 5.
Key ideas
- Two parts make one whole.
- Swap the parts and the total stays the same: 9 + 5 = 5 + 9.
- One fact gives you related facts: 9 + 5 = 14 means 14 − 5 = 9.
- To find a missing part, take the part you know away from the whole.
Key words. A number bond is two numbers that make a total. The whole is the total. The parts make the whole.
Method. Start from the whole. Take away the part you know to find the missing part.
- Find the whole and the part you know. The whole is the big number at the top of the picture.Whole: 14. Part I know: 9.
- Take the part you know away from the whole. Subtracting finds the missing part.14 − 9 = 5
- Write the missing part. 5
Check. Check: 9 + 5 = 14. ✓
Watch out. Start from the whole, not from the small number. Do not add the two parts together.
Key words. A number bond is two numbers that make a total. The whole is the total. The parts make the whole.
Method. Start from the whole. Take away the part you know to find the missing part.
- Find the whole and the part you know. The whole is the big number at the top of the picture.Whole: 20. Part I know: 12.
- Take the part you know away from the whole. Subtracting finds the missing part.20 − 12 = 8
- Write the missing part. 8
Check. Check: 12 + 8 = 20. ✓
Watch out. Start from the whole, not from the small number. Do not add the two parts together.
Key words. A fact family is four facts that use the same three numbers.
Method. Two parts make one whole. Each part can be found by taking the other part away from the whole.
- Put the two parts together, both ways. Adding the parts in either order gives the same whole.6 + 9 = 15 and 9 + 6 = 15
- Take each part away from the whole. Each take-away fact finds the part that is left.15 − 6 = 9 and 15 − 9 = 6
- Write all four facts. 6 + 9 = 15, 9 + 6 = 15, 15 − 6 = 9, 15 − 9 = 6
Check. Check one fact: 6 + 9 = 15, so 15 − 9 = 6. ✓
Watch out. Keep the whole at the start of a take-away. Write 15 − 6, not 6 − 15.
Watch out
Watch out: to find a missing part, take the part you know away from the whole. Do not add the two numbers together.
Exam tip
Grown-up tip. Put 14 buttons or pasta shapes in a pile. Hide 9 of them in one hand and show the rest. Ask: “How many are in my hand?” Then swap hands and say the facts out loud.
Exercise 5A Number bonds to 20
Non-calculatorKey words. A number bond is two numbers that make a total. The whole is the total. The parts make the whole.
Method. Start from the whole. Take away the part you know to find the missing part.
- Find the whole and the part you know. The whole is the big number at the top of the picture.Whole: 10. Part I know: 4.
- Take the part you know away from the whole. Subtracting finds the missing part.10 − 4 = 6
- Write the missing part. 6
Check. Check: 4 + 6 = 10. ✓
Watch out. Start from the whole, not from the small number. Do not add the two parts together.
Key words. A number bond is two numbers that make a total. The whole is the total. The parts make the whole.
Method. Start from the whole. Take away the part you know to find the missing part.
- Find the whole and the part you know. The whole is the big number at the top of the picture.Whole: 13. Part I know: 8.
- Take the part you know away from the whole. Subtracting finds the missing part.13 − 8 = 5
- Write the missing part. 5
Check. Check: 8 + 5 = 13. ✓
Watch out. Start from the whole, not from the small number. Do not add the two parts together.
Key words. A number bond is two numbers that make a total. The whole is the total. The parts make the whole.
Method. Start from the whole. Take away the part you know to find the missing part.
- Find the whole and the part you know. The whole is the big number at the top of the picture.Whole: 17. Part I know: 9.
- Take the part you know away from the whole. Subtracting finds the missing part.17 − 9 = 8
- Write the missing part. 8
Check. Check: 9 + 8 = 17. ✓
Watch out. Start from the whole, not from the small number. Do not add the two parts together.
Key words. A number bond is two numbers that make a total. The whole is the total. The parts make the whole.
Method. Start from the whole. Take away the part you know to find the missing part.
- Find the whole and the part you know. The whole is the big number at the top of the picture.Whole: 20. Part I know: 11.
- Take the part you know away from the whole. Subtracting finds the missing part.20 − 11 = 9
- Write the missing part. 9
Check. Check: 11 + 9 = 20. ✓
Watch out. Start from the whole, not from the small number. Do not add the two parts together.
Key words. A number bond is two numbers that make a total. The whole is the total. The parts make the whole.
Method. Start from the whole. Take away the part you know to find the missing part.
- Find the whole and the part you know. The whole is the big number at the top of the picture.Whole: 16. Part I know: 7.
- Take the part you know away from the whole. Subtracting finds the missing part.16 − 7 = 9
- Write the missing part. 9
Check. Check: 7 + 9 = 16. ✓
Watch out. Start from the whole, not from the small number. Do not add the two parts together.
Key words. A number bond is two numbers that make a total. The whole is the total. The parts make the whole.
Method. Start from the whole. Take away the part you know to find the missing part.
- Find the whole and the part you know. The whole is the big number at the top of the picture.Whole: 14. Part I know: 8.
- Take the part you know away from the whole. Subtracting finds the missing part.14 − 8 = 6
- Write the missing part. 6
Check. Check: 8 + 6 = 14. ✓
Watch out. Start from the whole, not from the small number. Do not add the two parts together.
Key words. A number bond is two numbers that make a total. The whole is the total. The parts make the whole.
Method. Start from the whole. Take away the part you know to find the missing part.
- Find the whole and the part you know. The whole is the big number at the top of the picture.Whole: 12. Part I know: 5.
- Take the part you know away from the whole. Subtracting finds the missing part.12 − 5 = 7
- Write the missing part. 7
Check. Check: 5 + 7 = 12. ✓
Watch out. Start from the whole, not from the small number. Do not add the two parts together.
Key words. A number bond is two numbers that make a total. The whole is the total. The parts make the whole.
Method. Start from the whole. Take away the part you know to find the missing part.
- Find the whole and the part you know. The whole is the big number at the top of the picture.Whole: 20. Part I know: 15.
- Take the part you know away from the whole. Subtracting finds the missing part.20 − 15 = 5
- Write the missing part. 5
Check. Check: 15 + 5 = 20. ✓
Watch out. Start from the whole, not from the small number. Do not add the two parts together.
Key words. A number bond is two numbers that make a total. The whole is the total. The parts make the whole.
Method. Start from the whole. Take away the part you know to find the missing part.
- Find the whole and the part you know. The whole is the big number at the top of the picture.Whole: 15. Part I know: 6.
- Take the part you know away from the whole. Subtracting finds the missing part.15 − 6 = 9
- Write the missing part. 9
Check. Check: 6 + 9 = 15. ✓
Watch out. Start from the whole, not from the small number. Do not add the two parts together.
Key words. A fact family is four facts that use the same three numbers.
Method. Two parts make one whole. Each part can be found by taking the other part away from the whole.
- Put the two parts together, both ways. Adding the parts in either order gives the same whole.7 + 8 = 15 and 8 + 7 = 15
- Take each part away from the whole. Each take-away fact finds the part that is left.15 − 7 = 8 and 15 − 8 = 7
- Write all four facts. 7 + 8 = 15, 8 + 7 = 15, 15 − 7 = 8, 15 − 8 = 7
Check. Check one fact: 7 + 8 = 15, so 15 − 8 = 7. ✓
Watch out. Keep the whole at the start of a take-away. Write 15 − 7, not 7 − 15.
Key words. A number bond is two numbers that make a total. The whole is the total. The parts make the whole.
Method. Start from the whole. Take away the part you know to find the missing part.
- Find the whole and the part you know. The whole is the big number at the top of the picture.Whole: 20. Part I know: 12.
- Take the part you know away from the whole. Subtracting finds the missing part.20 − 12 = 8
- Write the missing part. 8
Check. Check: 12 + 8 = 20. ✓
Watch out. Start from the whole, not from the small number. Do not add the two parts together.
Method. Swapping the two numbers does not change the total.
- Work out 14 + 6. Add the first number and the second number.14 + 6 = 20
- Now work out 6 + 14. Swap the numbers round and add again.6 + 14 = 20
- Compare the two totals. Are they the same?20 = 20
- Write the answer. No. Both give 20.
Check. Count on 6 from 14, or count on 14 from 6. You reach 20 both ways. ✓
Watch out. The order of the numbers does not change the total. Try another pair to check.
Method. Ruby knows that 9 + 5 = 14. Use that fact to check her answer.
- Look at what Ruby says. Ruby says 14 − 5 = 4.14 − 5 = 4 (Ruby)
- Use the fact she knows. The whole is 14 and one part is 5. The missing part is the other part.14 − 5 = 9
- Compare the answers. Ruby’s answer is not the same as the missing part.4 is not 9
- Write the answer. No. 14 − 5 = 9.
Check. Check: 9 + 5 = 14. ✓
Watch out. Ruby took away the wrong number. Take the part you know away from the whole.