Jumps of ten and one
You learn to jump on or back in tens and ones without counting.
How to work it out
- Check whether jumping by ten or one.
- Jumping by ten only changes the tens digit.
- Jumping by one changes the ones digit.
A worked example
52 + 10
- Jump on one ten.
- Only the tens digit changes: 5 becomes 6.
- So 52 + 10 = 62.
More examples
29 + 1
- Jump on one.
- After 29 comes the next ten.
- So 29 + 1 = 30.
60 − 1
- Jump back one.
- Before 60 comes 59.
- So 60 − 1 = 59.
Try it yourself
63 − 10 =
30 − 1 =
Watch out
When you jump on ten, you count on one: for 52 + 10 you say 53.
Look at the size of the jump. For ten, the tens digit changes; for one, the last digit changes.
For 60 − 1 you say 50 or 69.
One back from a round ten always ends in 9, in the ten below: from 60 to 59.
Tips
- When you jump on ten, the last digit stays the same.
- Jumping back one from a round number always gives a 9 at the end.
Exceptions
- For 95 + 10 you cross 100: the answer is 105.
Why it works
When you jump on one ten, only the tens digit changes: 52 becomes 62. When you jump on one, the ones digit changes. Sometimes you reach a new ten, like from 29 to 30. If you can see that, you will count much faster with big numbers later on.