Year 1: Adding and taking away to 20, including zero
Part of the Year 1 adding and subtracting within 20 chapter. Chapter overview · whole chapter on one page · Download worksheet (PDF) · Answers (PDF)
Adding and taking away to 20, including zero
To add a small number to a bigger one, start at the bigger number and count on. The picture shows 14 + 3. Start at 14. Count on 3: 15, 16, 17.
To take away, start at the whole and count back. Adding zero or taking away zero does not change the number. Zero means none.
Key ideas
- Count on from the bigger number to add.
- Count back from the whole to take away.
- Adding zero does not change the number: 12 + 0 = 12.
- Taking away zero does not change the number: 12 − 0 = 12.
Key words. To count on is to keep going up from a number, one at a time.
Method. Start with the bigger number, 14. Then count on 3.
- Start at 14. Start with the bigger number. You do not need to start at 1.Start: 14
- Count on 3 more. Say each number as you move one step on.15, 16, 17
- Write the answer. The last number you say is the answer.17
Check. Count back 3 from 17. You reach 14 again. ✓
Watch out. Count on from 14. Do not say 14 again as the first step.
Key words. To count on is to keep going up from a number, one at a time.
Method. Start with the bigger number, 13. Then count on 6.
- Start at 13. Start with the bigger number. You do not need to start at 1.Start: 13
- Count on 6 more. Say each number as you move one step on.14, 15, 16, 17, 18, 19
- Write the answer. The last number you say is the answer.19
Check. Count back 6 from 19. You reach 13 again. ✓
Watch out. Count on from 13. Do not say 13 again as the first step.
Key words. Zero means none at all. We write it as 0.
Method. Zero means none. Adding zero, or taking away zero, changes nothing.
- Look at the sum: 12 + 0. Find the zero in the sum.12 + 0
- Nothing is added or taken away. The number stays the same as it was.12 stays 12
- Write the answer. 12
Check. Count 12 things and take away none. You still have 12. ✓
Watch out. Zero does not change a number. Do not write 0 as the answer.
Watch out
Watch out: when you count on, do not say the starting number again. For 14 + 3, say 15, 16, 17. The answer is 17, not 18.
Exam tip
Grown-up tip. Use a number line, a 20-square or your fingers. Ask: “Start at 14. Count on 3. Where do you end?” Then count back again to check.
Exercise 5D Adding and taking away to 20
Non-calculatorKey words. To count on is to keep going up from a number, one at a time.
Method. Start with the bigger number, 11. Then count on 4.
- Start at 11. Start with the bigger number. You do not need to start at 1.Start: 11
- Count on 4 more. Say each number as you move one step on.12, 13, 14, 15
- Write the answer. The last number you say is the answer.15
Check. Count back 4 from 15. You reach 11 again. ✓
Watch out. Count on from 11. Do not say 11 again as the first step.
Key words. To count on is to keep going up from a number, one at a time.
Method. Start with the bigger number, 15. Then count on 2.
- Start at 15. Start with the bigger number. You do not need to start at 1.Start: 15
- Count on 2 more. Say each number as you move one step on.16, 17
- Write the answer. The last number you say is the answer.17
Check. Count back 2 from 17. You reach 15 again. ✓
Watch out. Count on from 15. Do not say 15 again as the first step.
Key words. To count on is to keep going up from a number, one at a time.
Method. Start with the bigger number, 10. Then count on 4.
- Start at 10. Start with the bigger number. You do not need to start at 1.Start: 10
- Count on 4 more. Say each number as you move one step on.11, 12, 13, 14
- Write the answer. The last number you say is the answer.14
Check. Count back 4 from 14. You reach 10 again. ✓
Watch out. Count on from 10. Do not say 10 again as the first step.
Key words. To count on is to keep going up from a number, one at a time.
Method. Start with the bigger number, 10. Then count on 9.
- Start at 10. Start with the bigger number. You do not need to start at 1.Start: 10
- Count on 9 more. Say each number as you move one step on.11, 12, 13, 14, 15, 16, 17, 18, 19
- Write the answer. The last number you say is the answer.19
Check. Count back 9 from 19. You reach 10 again. ✓
Watch out. Count on from 10. Do not say 10 again as the first step.
Key words. To count on is to keep going up from a number, one at a time.
Method. Start with the bigger number, 10. Then count on 7.
- Start at 10. Start with the bigger number. You do not need to start at 1.Start: 10
- Count on 7 more. Say each number as you move one step on.11, 12, 13, 14, 15, 16, 17
- Write the answer. The last number you say is the answer.17
Check. Count back 7 from 17. You reach 10 again. ✓
Watch out. Count on from 10. Do not say 10 again as the first step.
Key words. Zero means none at all. We write it as 0.
Method. Zero means none. Adding zero, or taking away zero, changes nothing.
- Look at the sum: 12 + 0. Find the zero in the sum.12 + 0
- Nothing is added or taken away. The number stays the same as it was.12 stays 12
- Write the answer. 12
Check. Count 12 things and take away none. You still have 12. ✓
Watch out. Zero does not change a number. Do not write 0 as the answer.
Key words. Zero means none at all. We write it as 0.
Method. Zero means none. Adding zero, or taking away zero, changes nothing.
- Look at the sum: 0 + 14. Find the zero in the sum.0 + 14
- Nothing is added or taken away. The number stays the same as it was.14 stays 14
- Write the answer. 14
Check. Count 14 things and take away none. You still have 14. ✓
Watch out. Zero does not change a number. Do not write 0 as the answer.
Key words. Zero means none at all. We write it as 0.
Method. Zero means none. Adding zero, or taking away zero, changes nothing.
- Look at the sum: 16 + 0. Find the zero in the sum.16 + 0
- Nothing is added or taken away. The number stays the same as it was.16 stays 16
- Write the answer. 16
Check. Count 16 things and take away none. You still have 16. ✓
Watch out. Zero does not change a number. Do not write 0 as the answer.
Key words. Zero means none at all. We write it as 0.
Method. Zero means none. Adding zero, or taking away zero, changes nothing.
- Look at the sum: 0 + 9. Find the zero in the sum.0 + 9
- Nothing is added or taken away. The number stays the same as it was.9 stays 9
- Write the answer. 9
Check. Count 9 things and take away none. You still have 9. ✓
Watch out. Zero does not change a number. Do not write 0 as the answer.
Key words. To take away is to remove some. To count back is to go down one at a time.
Method. Take away 3 from 16 by counting back 3 steps.
- Start at 16. Start with the whole amount.Start: 16
- Count back 3. Each step back is one less.15, 14, 13
- Write the answer. The last number you say is what is left.13
Check. Check: 13 + 3 = 16. ✓
Watch out. Count back, not on. Do not say the starting number as one of the steps.
Key words. To take away is to remove some. To count back is to go down one at a time.
Method. Take away 5 from 19 by counting back 5 steps.
- Start at 19. Start with the whole amount.Start: 19
- Count back 5. Each step back is one less.18, 17, 16, 15, 14
- Write the answer. The last number you say is what is left.14
Check. Check: 14 + 5 = 19. ✓
Watch out. Count back, not on. Do not say the starting number as one of the steps.
Key words. To take away is to remove some. To count back is to go down one at a time.
Method. Take away 4 from 18 by counting back 4 steps.
- Start at 18. Start with the whole amount.Start: 18
- Count back 4. Each step back is one less.17, 16, 15, 14
- Write the answer. The last number you say is what is left.14
Check. Check: 14 + 4 = 18. ✓
Watch out. Count back, not on. Do not say the starting number as one of the steps.
Key words. To take away is to remove some. To count back is to go down one at a time.
Method. Take away 2 from 13 by counting back 2 steps.
- Start at 13. Start with the whole amount.Start: 13
- Count back 2. Each step back is one less.12, 11
- Write the answer. The last number you say is what is left.11
Check. Check: 11 + 2 = 13. ✓
Watch out. Count back, not on. Do not say the starting number as one of the steps.
Key words. Zero means none at all. We write it as 0.
Method. Zero means none. Adding zero, or taking away zero, changes nothing.
- Look at the sum: 20 − 0. Find the zero in the sum.20 − 0
- Nothing is added or taken away. The number stays the same as it was.20 stays 20
- Write the answer. 20
Check. Count 20 things and take away none. You still have 20. ✓
Watch out. Zero does not change a number. Do not write 0 as the answer.
Key words. To count on is to keep going up from a number, one at a time.
Method. Start with the bigger number, 12. Then count on 7.
- Start at 12. Start with the bigger number. You do not need to start at 1.Start: 12
- Count on 7 more. Say each number as you move one step on.13, 14, 15, 16, 17, 18, 19
- Write the answer. The last number you say is the answer.19
Check. Count back 7 from 19. You reach 12 again. ✓
Watch out. Count on from 12. Do not say 12 again as the first step.
Key words. To take away is to remove some. To count back is to go down one at a time.
Method. Take away 5 from 17 by counting back 5 steps.
- Start at 17. Start with the whole amount.Start: 17
- Count back 5. Each step back is one less.16, 15, 14, 13, 12
- Write the answer. The last number you say is what is left.12
Check. Check: 12 + 5 = 17. ✓
Watch out. Count back, not on. Do not say the starting number as one of the steps.
Method. Taking away zero takes nothing away. The number stays the same.
- Look at the take-away. Sam takes away zero.15 − 0
- Think about what is taken away. Zero means none, so nothing leaves the group.Nothing is taken away
- Write the answer. No. 15 − 0 = 15.
Check. Count 15 things and take none away. You still have 15. ✓
Watch out. Zero does not change a number. Do not write 0 as the answer.