Step-by-step Maths Level 2 Number bonds to 20: check-up and practice test questions

Method. Find the part that makes 20 with the number we know.

1. Start with 7. It is the part we know.
   7
2. Find how far it is to 20. Take the known part away from the whole, 20.
   20 - 7 = 13
3. Write the answer. This is the other part of the bond.
   13

Check. 7 + 13 = 20. It works.

Watch out. The whole is 20, so take the known part away from 20.

Method. Find the missing part of the addition.

1. Look at the 7 we know. It is one of the two parts.
   7
2. Count on or take away from 20. The missing part is the rest of 20.
   20 - 7 = 13
3. Write the missing number.
   13

Check. 7 + 13 = 20. It works.

Watch out. The whole is 20. The missing part is what is left after you take away the known part.

Method. Use a bond to 10 to help. Start from 20 and take away the tens first.

1. Take 10 away from 20. That leaves 10.
   20 - 10 = 10
2. Take the rest of 17 away from 10. 17 is 10 and 7, so take away 7 from 10.
   10 - 7 = 3
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. Find the part that makes 20 with the number we know.

1. Start with 18. It is the part we know.
   18
2. Find how far it is to 20. Take the known part away from the whole, 20.
   20 - 18 = 2
3. Write the answer. This is the other part of the bond.
   2

Check. 18 + 2 = 20. It works.

Watch out. The whole is 20, so take the known part away from 20.

Method. Use a bond to 10 to help. Start from 20 and take away the tens first.

1. Take 10 away from 20. That leaves 10.
   20 - 10 = 10
2. Take the rest of 13 away from 10. 13 is 10 and 3, so take away 3 from 10.
   10 - 3 = 7
3. 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. In a part-whole picture, the two parts add up to the whole.

1. Look at the whole and the known part. The whole is 20.
   20 and 19
2. Take the known part away from the whole. What is left is the missing part.
   20 - 19 = 1
3. Write the missing part.
   1

Check. 19 and 1 make 20. It works.

Watch out. The missing part is never the whole. Find the part by subtracting.

Method. In a part-whole picture, the two parts add up to the whole.

1. Look at the whole and the known part. The whole is 20.
   20 and 2
2. Take the known part away from the whole. What is left is the missing part.
   20 - 2 = 18
3. Write the missing part.
   18

Check. 2 and 18 make 20. It works.

Watch out. The missing part is never the whole. Find the part by subtracting.

Method. Use a bond to 10 to help. Start from 20 and take away the tens first.

1. Take 10 away from 20. That leaves 10.
   20 - 10 = 10
2. Take the rest of 15 away from 10. 15 is 10 and 5, so take away 5 from 10.
   10 - 5 = 5
3. 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.

1. Take 10 away from 20. That leaves 10.
   20 - 10 = 10
2. Take the rest of 19 away from 10. 19 is 10 and 9, so take away 9 from 10.
   10 - 9 = 1
3. 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. Find the missing part of the addition.

1. Look at the 19 we know. It is one of the two parts.
   19
2. Count on or take away from 20. The missing part is the rest of 20.
   20 - 19 = 1
3. Write the missing number.
   1

Check. 19 + 1 = 20. It works.

Watch out. The whole is 20. The missing part is what is left after you take away the known part.

Method. A fact family has an addition and a subtraction with the same numbers.

1. Read the addition fact. It has two parts and a whole.
   5 + 15 = 20
2. Use the whole, 20, to make the subtraction. Take one part away from the whole to find the other part.
   20 - 5 = 15
3. Write the answer. The other part is the answer.
   15

Check. 5 + 15 = 20 and 20 - 5 = 15 use the same numbers.

Watch out. The subtraction takes away a part from the whole, so the answer is the other part.

Method. Use a bond to 10 to help. Start from 20 and take away the tens first.

1. Take 10 away from 20. That leaves 10.
   20 - 10 = 10
2. Take the rest of 14 away from 10. 14 is 10 and 4, so take away 4 from 10.
   10 - 4 = 6
3. 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. Find the missing part of the addition.

1. Look at the 2 we know. It is one of the two parts.
   2
2. Count on or take away from 20. The missing part is the rest of 20.
   20 - 2 = 18
3. Write the missing number.
   18

Check. 2 + 18 = 20. It works.

Watch out. The whole is 20. The missing part is what is left after you take away the known part.

Method. Find the part that makes 20 with the number we know.

1. Start with 1. It is the part we know.
   1
2. Find how far it is to 20. Take the known part away from the whole, 20.
   20 - 1 = 19
3. Write the answer. This is the other part of the bond.
   19

Check. 1 + 19 = 20. It works.

Watch out. The whole is 20, so take the known part away from 20.

Method. Use a bond to 10 to help. Start from 20 and take away the tens first.

1. Take 10 away from 20. That leaves 10.
   20 - 10 = 10
2. Take the rest of 12 away from 10. 12 is 10 and 2, so take away 2 from 10.
   10 - 2 = 8
3. 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. In a part-whole picture, the two parts add up to the whole.

1. Look at the whole and the known part. The whole is 20.
   20 and 2
2. Take the known part away from the whole. What is left is the missing part.
   20 - 2 = 18
3. Write the missing part.
   18

Check. 2 and 18 make 20. It works.

Watch out. The missing part is never the whole. Find the part by subtracting.

Method. Use a bond to 10 to help. Start from 20 and take away the tens first.

1. Take 10 away from 20. That leaves 10.
   20 - 10 = 10
2. Take the rest of 19 away from 10. 19 is 10 and 9, so take away 9 from 10.
   10 - 9 = 1
3. 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. In a part-whole picture, the two parts add up to the whole.

1. Look at the whole and the known part. The whole is 20.
   20 and 8
2. Take the known part away from the whole. What is left is the missing part.
   20 - 8 = 12
3. Write the missing part.
   12

Check. 8 and 12 make 20. It works.

Watch out. The missing part is never the whole. Find the part by subtracting.

Method. Find the part that makes 20 with the number we know.

1. Start with 2. It is the part we know.
   2
2. Find how far it is to 20. Take the known part away from the whole, 20.
   20 - 2 = 18
3. Write the answer. This is the other part of the bond.
   18

Check. 2 + 18 = 20. It works.

Watch out. The whole is 20, so take the known part away from 20.

Method. Find the missing part of the addition.

1. Look at the 1 we know. It is one of the two parts.
   1
2. Count on or take away from 20. The missing part is the rest of 20.
   20 - 1 = 19
3. Write the missing number.
   19

Check. 1 + 19 = 20. It works.

Watch out. The whole is 20. The missing part is what is left after you take away the known part.