Step-by-step Maths Level 2: Using bonds to 10 to find bonds to 20
Part of the Step-by-step Maths Level 2 number bonds to 20 chapter. Chapter overview · whole chapter on one page
Using bonds to 10 to find bonds to 20
You already know the bonds to 10. Use them to find bonds to 20.
Take 10 away from 20 first. Then take the rest away from 10. This is quicker than counting on.
Key ideas
- Bonds to 10 help with bonds to 20.
- Take 10 away from 20 first.
- Then take the rest away from 10.
Method. Use a bond to 10 to help. Start from 20 and take away the tens first.
- Take 10 away from 20. That leaves 10.20 - 10 = 10
- Take the rest of 16 away from 10. 16 is 10 and 6, so take away 6 from 10.10 - 6 = 4
- Write the answer. This is the missing part.4
Check. 16 + 4 = 20. Also 10 + 6 + 4 = 20.
Watch out. Use the bond 10 and 10 first. Then the rest is only a small step.
Method. Use a bond to 10 to help. Start from 20 and take away the tens first.
- Take 10 away from 20. That leaves 10.20 - 10 = 10
- Take the rest of 12 away from 10. 12 is 10 and 2, so take away 2 from 10.10 - 2 = 8
- Write the answer. This is the missing part.8
Check. 12 + 8 = 20. Also 10 + 2 + 8 = 20.
Watch out. Use the bond 10 and 10 first. Then the rest is only a small step.
Method. Use a bond to 10 to help. Start from 20 and take away the tens first.
- Take 10 away from 20. That leaves 10.20 - 10 = 10
- Take the rest of 19 away from 10. 19 is 10 and 9, so take away 9 from 10.10 - 9 = 1
- Write the answer. This is the missing part.1
Check. 19 + 1 = 20. Also 10 + 9 + 1 = 20.
Watch out. Use the bond 10 and 10 first. Then the rest is only a small step.
Watch out
Watch out. Take the rest away from 10, not from 20 again. 20 - 10 = 10 is the first step only.
Exam tip
Grown-up tip. Ask: “How many more to make ten?” Then “How many more to make twenty?”
Exercise 4B Practice: bonds to 20 with bonds to 10
Non-calculatorMethod. Use a bond to 10 to help. Start from 20 and take away the tens first.
- Take 10 away from 20. That leaves 10.20 - 10 = 10
- Take the rest of 15 away from 10. 15 is 10 and 5, so take away 5 from 10.10 - 5 = 5
- Write the answer. This is the missing part.5
Check. 15 + 5 = 20. Also 10 + 5 + 5 = 20.
Watch out. Use the bond 10 and 10 first. Then the rest is only a small step.
Method. Use a bond to 10 to help. Start from 20 and take away the tens first.
- Take 10 away from 20. That leaves 10.20 - 10 = 10
- Take the rest of 11 away from 10. 11 is 10 and 1, so take away 1 from 10.10 - 1 = 9
- Write the answer. This is the missing part.9
Check. 11 + 9 = 20. Also 10 + 1 + 9 = 20.
Watch out. Use the bond 10 and 10 first. Then the rest is only a small step.
Method. Use a bond to 10 to help. Start from 20 and take away the tens first.
- Take 10 away from 20. That leaves 10.20 - 10 = 10
- Take the rest of 16 away from 10. 16 is 10 and 6, so take away 6 from 10.10 - 6 = 4
- Write the answer. This is the missing part.4
Check. 16 + 4 = 20. Also 10 + 6 + 4 = 20.
Watch out. Use the bond 10 and 10 first. Then the rest is only a small step.
Method. Use a bond to 10 to help. Start from 20 and take away the tens first.
- Take 10 away from 20. That leaves 10.20 - 10 = 10
- Take the rest of 12 away from 10. 12 is 10 and 2, so take away 2 from 10.10 - 2 = 8
- Write the answer. This is the missing part.8
Check. 12 + 8 = 20. Also 10 + 2 + 8 = 20.
Watch out. Use the bond 10 and 10 first. Then the rest is only a small step.
Method. Use a bond to 10 to help. Start from 20 and take away the tens first.
- Take 10 away from 20. That leaves 10.20 - 10 = 10
- Take the rest of 19 away from 10. 19 is 10 and 9, so take away 9 from 10.10 - 9 = 1
- Write the answer. This is the missing part.1
Check. 19 + 1 = 20. Also 10 + 9 + 1 = 20.
Watch out. Use the bond 10 and 10 first. Then the rest is only a small step.
Method. Use a bond to 10 to help. Start from 20 and take away the tens first.
- Take 10 away from 20. That leaves 10.20 - 10 = 10
- Take the rest of 17 away from 10. 17 is 10 and 7, so take away 7 from 10.10 - 7 = 3
- Write the answer. This is the missing part.3
Check. 17 + 3 = 20. Also 10 + 7 + 3 = 20.
Watch out. Use the bond 10 and 10 first. Then the rest is only a small step.
Method. Use a bond to 10 to help. Start from 20 and take away the tens first.
- Take 10 away from 20. That leaves 10.20 - 10 = 10
- Take the rest of 13 away from 10. 13 is 10 and 3, so take away 3 from 10.10 - 3 = 7
- Write the answer. This is the missing part.7
Check. 13 + 7 = 20. Also 10 + 3 + 7 = 20.
Watch out. Use the bond 10 and 10 first. Then the rest is only a small step.
Method. Use a bond to 10 to help. Start from 20 and take away the tens first.
- Take 10 away from 20. That leaves 10.20 - 10 = 10
- Take the rest of 14 away from 10. 14 is 10 and 4, so take away 4 from 10.10 - 4 = 6
- Write the answer. This is the missing part.6
Check. 14 + 6 = 20. Also 10 + 4 + 6 = 20.
Watch out. Use the bond 10 and 10 first. Then the rest is only a small step.
Method. Use a bond to 10 to help. Start from 20 and take away the tens first.
- Take 10 away from 20. That leaves 10.20 - 10 = 10
- Take the rest of 18 away from 10. 18 is 10 and 8, so take away 8 from 10.10 - 8 = 2
- Write the answer. This is the missing part.2
Check. 18 + 2 = 20. Also 10 + 8 + 2 = 20.
Watch out. Use the bond 10 and 10 first. Then the rest is only a small step.