Reception Maths: Counting on and back to 20

Method. Find 19 on the number track. The number after it is the answer.

1. Find 19. Put your finger on it.
   19
2. Move one box to the right. Each box is one more or one less.
   19 + 1 = 20
3. Write the answer.
   20

Check. Check it: 20 − 1 = 19. ✓

Watch out. Move one box only. Do not write the number you started with.

Method. Find 12 on the number track. The number before it is the answer.

1. Find 12. Put your finger on it.
   12
2. Move one box to the left. Each box is one more or one less.
   12 − 1 = 11
3. Write the answer.
   11

Check. Check it: 11 + 1 = 12. ✓

Watch out. Move one box only. Do not write the number you started with.

Method. Start at 5 and count on to 9. Each number is one more than the one before.

1. Start at 5. Say the first number.
   5
2. Count on to 9. Say each number, one more each time.
   5, 6, 7, 8, 9
3. Write the numbers. Write them in order.
   5, 6, 7, 8, 9

Check. Count back from 9 to 5. You say the same numbers in reverse. ✓

Watch out. Do not skip a number. Check each one is one more than the last.

Method. Start at 15 and count back to 12. Each number is one less than the one before.

1. Start at 15. Start with the biggest number.
   15
2. Count back to 12. Each number is one less.
   15, 14, 13, 12
3. Write the numbers. Include the first and last numbers.
   15, 14, 13, 12

Check. Count on from 12 to 15 to check. ✓

Watch out. Count back one at a time. Do not jump over a number.

Method. Each number is one more than the number before. Use the numbers you can see to find the gaps.

1. Look at the numbers around each gap. Counting on means each number is one more.
   11, ?, 13, ?, 15
2. Add one to the number before each gap. That gives the missing number.
   Gap 2: 11 + 1 = 12
   Gap 4: 13 + 1 = 14
3. Write the missing numbers.
   12, 14

Check. Read the whole line again. Every 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. Each number is one more than the number before. Use the numbers you can see to find the gaps.

1. Look at the numbers around each gap. Counting on means each number is one more.
   16, 17, ?, 19
2. Add one to the number before each gap. That gives the missing number.
   Gap 3: 17 + 1 = 18
3. Write the missing numbers.
   18

Check. Read the whole line again. Every 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 17 and count on to 20. Each number is one more than the one before.

1. Start at 17. Say the first number.
   17
2. Count on to 20. Say each number, one more each time.
   17, 18, 19, 20
3. Write the numbers. Write them in order.
   17, 18, 19, 20

Check. Count back from 20 to 17. You say the same numbers in reverse. ✓

Watch out. Do not skip a number. Check each one is one more than the last.

Method. Start at 20 and count back to 16. Each number is one less than the one before.

1. Start at 20. Start with the biggest number.
   20
2. Count back to 16. Each number is one less.
   20, 19, 18, 17, 16
3. Write the numbers. Include the first and last numbers.
   20, 19, 18, 17, 16

Check. Count on from 16 to 20 to check. ✓

Watch out. Count back one at a time. Do not jump over a number.

Method. Find 6 on the number track. The number after it is the answer.

1. Find 6. Put your finger on it.
   6
2. Move one box to the right. Each box is one more or one less.
   6 + 1 = 7
3. Write the answer.
   7

Check. Check it: 7 − 1 = 6. ✓

Watch out. Move one box only. Do not write the number you started with.

Method. Find 10 on the number track. The number before it is the answer.

1. Find 10. Put your finger on it.
   10
2. Move one box to the left. Each box is one more or one less.
   10 − 1 = 9
3. Write the answer.
   9

Check. Check it: 9 + 1 = 10. ✓

Watch out. Move one box only. Do not write the number you started with.

Method. Start at 12 on the track. Count on 4 boxes, one at a time.

1. Start at 12. Put your finger on 12.
   12
2. Count on 4 boxes. Say each number as you move one box.
   13, 14, 15, 16
3. Write the answer. The last number you said is the answer.
   16

Check. Count back 4 from 16: 15, 14, 13, 12. You are back at 12. ✓

Watch out. Count on from 12, not from 13.

Method. Start at 18 and count back to 13. Each number is one less than the one before.

1. Start at 18. Start with the biggest number.
   18
2. Count back to 13. Each number is one less.
   18, 17, 16, 15, 14, 13
3. Write the numbers. Include the first and last numbers.
   18, 17, 16, 15, 14, 13

Check. Count on from 13 to 18 to check. ✓

Watch out. Count back one at a time. Do not jump over a number.

Method. Start at 16 and count on to 20. Each number is one more than the one before.

1. Start at 16. Say the first number.
   16
2. Count on to 20. Say each number, one more each time.
   16, 17, 18, 19, 20
3. Write the numbers. Write them in order.
   16, 17, 18, 19, 20

Check. Count back from 20 to 16. You say the same numbers in reverse. ✓

Watch out. Do not skip a number. Check each one is one more than the last.

Method. Count back from 20 to 15, one number at a time. Then count how many numbers you said.

1. Count back from 20 to 15. Say each number as you go down.
   20, 19, 18, 17, 16, 15
2. Count the numbers you said. Touch each number once.
   1, 2, 3, 4, 5, 6
3. Write the answer.
   Yes. There are 6 numbers from 20 down to 15.

Check. Count 15 to 20: 15, 16, 17, 18, 19, 20. Six numbers. ✓

Watch out. Count both ends, 20 and 15.