Step-by-step Maths Level 2 Taking away within 20: check-up and practice test questions

Method. The difference is how far apart the numbers are. Count up from the smaller number.

1. Start at the smaller number, 3. We count up to the bigger number.
   3
2. Count up to 17. Count each step as you go.
   17 - 3 = 14
3. Write the difference. The number of steps is the difference.
   14

Check. 3 + 14 = 17. The difference is right.

Watch out. The difference is not the bigger number. It is the number of steps between them.

Method. The difference is how far apart the numbers are. Count up from the smaller number.

1. Start at the smaller number, 8. We count up to the bigger number.
   8
2. Count up to 18. Count each step as you go.
   18 - 8 = 10
3. Write the difference. The number of steps is the difference.
   10

Check. 8 + 10 = 18. The difference is right.

Watch out. The difference is not the bigger number. It is the number of steps between them.

Method. Use a bond to 10 to help. Take away the part that gets to 10 first.

1. Take 1 away from 11. That leaves exactly 10.
   11 - 1 = 10
2. Take the rest, 3, away from 10. 4 is 1 and 3, so take away 3 now.
   10 - 3 = 7
3. Write the answer.
   7

Check. Add back: 7 + 4 = 11. It is right.

Watch out. Going through 10 can be done in two steps. Do not take the whole number from 10 by mistake.

Method. Work out the subtraction. Then add the number you took away to the answer.

1. Work out 16 - 9. Count back from the first number.
   16 - 9 = 7
2. Check by adding. If the answer is right, adding back gives the first number.
   7 + 9 = 16
3. Write the answer.
   7

Check. 7 + 9 = 16, so the answer is right.

Watch out. Subtraction and addition undo each other. Use addition to check.

Method. Start at the first number and count back the second number.

1. Start at 20. It is the number we begin with.
   20
2. Count back 5. Say each number as you go back.
   20 - 5 = 15
3. Write the answer. This is how many are left.
   15

Check. Count on 5 from 15 to check: you reach 20.

Watch out. Count back from the first number. Do not count the starting number again.

Method. Taking away 10 takes away one ten. Only the tens digit changes.

1. Look at the number. It has one ten and some ones.
   13
2. Take away one ten. Take away 10 from the tens.
   13 - 10 = 3
3. Write the answer. The ones stay the same.
   3

Check. Add 10 back: 3 + 10 = 13.

Watch out. Taking away 10 changes the tens, not the ones: 17 - 10 = 7.

Method. Taking away 10 takes away one ten. Only the tens digit changes.

1. Look at the number. It has one ten and some ones.
   16
2. Take away one ten. Take away 10 from the tens.
   16 - 10 = 6
3. Write the answer. The ones stay the same.
   6

Check. Add 10 back: 6 + 10 = 16.

Watch out. Taking away 10 changes the tens, not the ones: 17 - 10 = 7.

Method. Start at the first number and count back the second number.

1. Start at 15. It is the number we begin with.
   15
2. Count back 9. Say each number as you go back.
   15 - 9 = 6
3. Write the answer. This is how many are left.
   6

Check. Count on 9 from 6 to check: you reach 15.

Watch out. Count back from the first number. Do not count the starting number again.

Method. Start at the first number and count back the second number.

1. Start at 12. It is the number we begin with.
   12
2. Count back 8. Say each number as you go back.
   12 - 8 = 4
3. Write the answer. This is how many are left.
   4

Check. Count on 8 from 4 to check: you reach 12.

Watch out. Count back from the first number. Do not count the starting number again.

Method. Use a bond to 10 to help. Take away the part that gets to 10 first.

1. Take 2 away from 12. That leaves exactly 10.
   12 - 2 = 10
2. Take the rest, 4, away from 10. 6 is 2 and 4, so take away 4 now.
   10 - 4 = 6
3. Write the answer.
   6

Check. Add back: 6 + 6 = 12. It is right.

Watch out. Going through 10 can be done in two steps. Do not take the whole number from 10 by mistake.

Method. Find the number to take away. Check by adding it back.

1. Start with 11. It is the number we begin with.
   11
2. Find how many are taken away to reach 3. Count back, or take the answer away from the start.
   11 - 3 = 8
3. Write the missing number.
   8

Check. Add back: 3 + 8 = 11. It works.

Watch out. The missing number is the one that gets you from the start to the answer.

Method. Find the number to take away. Check by adding it back.

1. Start with 8. It is the number we begin with.
   8
2. Find how many are taken away to reach 7. Count back, or take the answer away from the start.
   8 - 7 = 1
3. Write the missing number.
   1

Check. Add back: 7 + 1 = 8. It works.

Watch out. The missing number is the one that gets you from the start to the answer.

Method. The difference is how far apart the numbers are. Count up from the smaller number.

1. Start at the smaller number, 3. We count up to the bigger number.
   3
2. Count up to 19. Count each step as you go.
   19 - 3 = 16
3. Write the difference. The number of steps is the difference.
   16

Check. 3 + 16 = 19. The difference is right.

Watch out. The difference is not the bigger number. It is the number of steps between them.

Method. Start at the first number and count back the second number.

1. Start at 20. It is the number we begin with.
   20
2. Count back 7. Say each number as you go back.
   20 - 7 = 13
3. Write the answer. This is how many are left.
   13

Check. Count on 7 from 13 to check: you reach 20.

Watch out. Count back from the first number. Do not count the starting number again.

Method. The difference is how far apart the numbers are. Count up from the smaller number.

1. Start at the smaller number, 5. We count up to the bigger number.
   5
2. Count up to 8. Count each step as you go.
   8 - 5 = 3
3. Write the difference. The number of steps is the difference.
   3

Check. 5 + 3 = 8. The difference is right.

Watch out. The difference is not the bigger number. It is the number of steps between them.

Method. Find the number to take away. Check by adding it back.

1. Start with 20. It is the number we begin with.
   20
2. Find how many are taken away to reach 3. Count back, or take the answer away from the start.
   20 - 3 = 17
3. Write the missing number.
   17

Check. Add back: 3 + 17 = 20. It works.

Watch out. The missing number is the one that gets you from the start to the answer.

Method. Use a bond to 10 to help. Take away the part that gets to 10 first.

1. Take 5 away from 15. That leaves exactly 10.
   15 - 5 = 10
2. Take the rest, 2, away from 10. 7 is 5 and 2, so take away 2 now.
   10 - 2 = 8
3. Write the answer.
   8

Check. Add back: 8 + 7 = 15. It is right.

Watch out. Going through 10 can be done in two steps. Do not take the whole number from 10 by mistake.

Method. Use a bond to 10 to help. Take away the part that gets to 10 first.

1. Take 5 away from 15. That leaves exactly 10.
   15 - 5 = 10
2. Take the rest, 4, away from 10. 9 is 5 and 4, so take away 4 now.
   10 - 4 = 6
3. Write the answer.
   6

Check. Add back: 6 + 9 = 15. It is right.

Watch out. Going through 10 can be done in two steps. Do not take the whole number from 10 by mistake.

Method. The difference is how far apart the numbers are. Count up from the smaller number.

1. Start at the smaller number, 6. We count up to the bigger number.
   6
2. Count up to 14. Count each step as you go.
   14 - 6 = 8
3. Write the difference. The number of steps is the difference.
   8

Check. 6 + 8 = 14. The difference is right.

Watch out. The difference is not the bigger number. It is the number of steps between them.

Method. Work out the subtraction. Then add the number you took away to the answer.

1. Work out 6 - 5. Count back from the first number.
   6 - 5 = 1
2. Check by adding. If the answer is right, adding back gives the first number.
   1 + 5 = 6
3. Write the answer.
   1

Check. 1 + 5 = 6, so the answer is right.

Watch out. Subtraction and addition undo each other. Use addition to check.