Year 1: One more, one less and the number line to 20
Part of the Year 1 numbers to 20 chapter. Chapter overview · whole chapter on one page · Download worksheet (PDF) · Answers (PDF)
One more, one less and the number line to 20
The number line goes from 0 on the left to 20 on the right. Each number is one step further right than the number before it.
One more is the next number, one step to the right. One less is the number just before, one step to the left.
The same rule works past ten. One more than 19 is 20. One less than 11 is 10.
Key ideas
- One more is the next number on the right.
- One less is the number before, on the left.
- One more than 19 is 20.
- Use the number line, or ten frames, to check.
Key words. One more is the next number. One less is the number just before.
Method. Start at 15. One more is the number after 15.
- Start at 15. Put your finger on the number.Start: 15
- Move one step forward. Each step on the number line is one number.15 + 1 = 16
- Write the answer. 16
Check. Check it: 16 − 1 = 15. ✓
Watch out. Move one step, not two. Do not write the number you started with.
Key words. One more is the next number. One less is the number just before.
Method. Start at 20. One less is the number before 20.
- Start at 20. Put your finger on the number.Start: 20
- Move one step back. Each step on the number line is one number.20 − 1 = 19
- Write the answer. 19
Check. Check it: 19 + 1 = 20. ✓
Watch out. Move one step, not two. Do not write the number you started with.
Method. Each number is one more than the number before it. Use the numbers you can see to find the gaps.
- Look at the numbers before each gap. Counting on in ones means each number is one more than the one before.16, 17, ?, 19
- Count on one from the number before each gap. Add 1 to the number before the gap.Gap 3: 17 + 1 = 18
- Write the missing numbers. 18
Check. Read the whole line again: each number is one more than the one before. ✓
Watch out. Check the numbers after the gap too. They should still go up by one.
Watch out
Watch out: one more than 19 is 20. Do not write the digits 1 and 9 again, and do not write 19 again. Write the next number.
Exam tip
Grown-up tip. Draw a number line from 0 to 20 on paper. Put a finger on a number. Say “one more” and move one step right. Then say “one less” and move one step left.
Exercise 4D One more, one less and moving along
Non-calculatorKey words. One more is the next number. One less is the number just before.
Method. Start at 12. One more is the number after 12.
- Start at 12. Put your finger on the number.Start: 12
- Move one step forward. Each step on the number line is one number.12 + 1 = 13
- Write the answer. 13
Check. Check it: 13 − 1 = 12. ✓
Watch out. Move one step, not two. Do not write the number you started with.
Key words. One more is the next number. One less is the number just before.
Method. Start at 16. One more is the number after 16.
- Start at 16. Put your finger on the number.Start: 16
- Move one step forward. Each step on the number line is one number.16 + 1 = 17
- Write the answer. 17
Check. Check it: 17 − 1 = 16. ✓
Watch out. Move one step, not two. Do not write the number you started with.
Key words. One more is the next number. One less is the number just before.
Method. Start at 19. One more is the number after 19.
- Start at 19. Put your finger on the number.Start: 19
- Move one step forward. Each step on the number line is one number.19 + 1 = 20
- Write the answer. 20
Check. Check it: 20 − 1 = 19. ✓
Watch out. Move one step, not two. Do not write the number you started with.
Key words. One more is the next number. One less is the number just before.
Method. Start at 14. One less is the number before 14.
- Start at 14. Put your finger on the number.Start: 14
- Move one step back. Each step on the number line is one number.14 − 1 = 13
- Write the answer. 13
Check. Check it: 13 + 1 = 14. ✓
Watch out. Move one step, not two. Do not write the number you started with.
Key words. One more is the next number. One less is the number just before.
Method. Start at 20. One less is the number before 20.
- Start at 20. Put your finger on the number.Start: 20
- Move one step back. Each step on the number line is one number.20 − 1 = 19
- Write the answer. 19
Check. Check it: 19 + 1 = 20. ✓
Watch out. Move one step, not two. Do not write the number you started with.
Key words. One more is the next number. One less is the number just before.
Method. Start at 11. One less is the number before 11.
- Start at 11. Put your finger on the number.Start: 11
- Move one step back. Each step on the number line is one number.11 − 1 = 10
- Write the answer. 10
Check. Check it: 10 + 1 = 11. ✓
Watch out. Move one step, not two. Do not write the number you started with.
Key words. One more is the next number. One less is the number just before.
Method. Start at 9. One more is the number after 9.
- Start at 9. Put your finger on the number.Start: 9
- Move one step forward. Each step on the number line is one number.9 + 1 = 10
- Write the answer. 10
Check. Check it: 10 − 1 = 9. ✓
Watch out. Move one step, not two. Do not write the number you started with.
Key words. One more is the next number. One less is the number just before.
Method. Start at 10. One less is the number before 10.
- Start at 10. Put your finger on the number.Start: 10
- Move one step back. Each step on the number line is one number.10 − 1 = 9
- Write the answer. 9
Check. Check it: 9 + 1 = 10. ✓
Watch out. Move one step, not two. Do not write the number you started with.
Method. Each number is one more than the number before it. Use the numbers you can see to find the gaps.
- Look at the numbers before each gap. Counting on in ones means each number is one more than the one before.0, 1, 2, 3, 4, 5, 6, ?, 8, 9, 10, 11, 12, 13, 14, ?, 16, 17, 18, 19, 20
- Count on one from the number before each gap. Add 1 to the number before the gap.Gap 8: 6 + 1 = 7
Gap 16: 14 + 1 = 15 - Write the missing numbers. 7, 15
Check. Read the whole line again: each number is one more than the one before. ✓
Watch out. Check the numbers after the gap too. They should still go up by one.
Method. Start at 13. Move one step at a time, forwards.
- Start at 13. Put your finger on the start number.13
- Move 1 step forward. Say each number as you land on it.13, 14
- Write where you end up. The last number is where you finish.14
Check. Count the steps again: you took 1 step. ✓
Watch out. Count the steps, not the numbers. The start number is not a step.
Method. Start at 18. Move one step at a time, backwards.
- Start at 18. Put your finger on the start number.18
- Move 2 steps backwards. Say each number as you land on it.18, 17, 16
- Write where you end up. The last number is where you finish.16
Check. Count the steps again: you took 2 steps. ✓
Watch out. Count the steps, not the numbers. The start number is not a step.
Method. Start at 5. Move one step at a time, forwards.
- Start at 5. Put your finger on the start number.5
- Move 3 steps forwards. Say each number as you land on it.5, 6, 7, 8
- Write where you end up. The last number is where you finish.8
Check. Count the steps again: you took 3 steps. ✓
Watch out. Count the steps, not the numbers. The start number is not a step.
Key words. One more is the next number. One less is the number just before.
Method. Start at 14. One more is the number after 14.
- Start at 14. Put your finger on the number.Start: 14
- Move one step forward. Each step on the number line is one number.14 + 1 = 15
- Write the answer. 15
Check. Check it: 15 − 1 = 14. ✓
Watch out. Move one step, not two. Do not write the number you started with.
Key words. One more is the next number. One less is the number just before.
Method. Start at 17. One less is the number before 17.
- Start at 17. Put your finger on the number.Start: 17
- Move one step back. Each step on the number line is one number.17 − 1 = 16
- Write the answer. 16
Check. Check it: 16 + 1 = 17. ✓
Watch out. Move one step, not two. Do not write the number you started with.
Key words. One more is the next number. One less is the number just before.
Method. Start at 20. One less is the number before 20.
- Start at 20. Put your finger on the number.Start: 20
- Move one step back. Each step on the number line is one number.20 − 1 = 19
- Write the answer. 19
Check. Check it: 19 + 1 = 20. ✓
Watch out. Move one step, not two. Do not write the number you started with.
Method. Count on one from 19 on the number line. The next number is 20.
- Start at 19. Find 19 on the number line.19
- Move one step right. One more is the next number on the right.19 + 1 = 20
- Compare with Ben’s answer. The next number is 20, not 91. The digits 9 and 1 do not come next.20
Check. Count on from 19: the next number is 20. ✓
Watch out. One more adds one. It does not join the digits together.
Method. Each number is one more than the number before it. Use the numbers you can see to find the gaps.
- Look at the numbers before each gap. Counting on in ones means each number is one more than the one before.17, 18, 19, ?, 21
- Count on one from the number before each gap. Add 1 to the number before the gap.Gap 4: 19 + 1 = 20
- Write the missing numbers. 20
Check. Read the whole line again: each number is one more than the one before. ✓
Watch out. Check the numbers after the gap too. They should still go up by one.