The four quick moves
Some changes to a number are so useful they’re worth knowing by heart:
| Move | What changes | 47 becomes |
|---|---|---|
| One more | Ones digit goes up 1 | 48 |
| One less | Ones digit goes down 1 | 46 |
| Ten more | Tens digit goes up 1 | 57 |
| Ten less | Tens digit goes down 1 | 37 |
Notice: adding or taking away ten leaves the ones digit the same. Only the tens digit changes.
Seeing it on a hundred chart
On a hundred chart:
- One step right = one more.
- One step left = one less.
- One step down = ten more.
- One step up = ten less.
| 36 | 37 | 38 |
|---|---|---|
| 46 | 47 | 48 |
| 56 | 57 | 58 |
Around 47, the numbers are 46 (left), 48 (right), 37 (above) and 57 (below).
Seeing it with base-ten blocks
47 is 4 ten-rods and 7 unit cubes. Add one more rod and you have 5 rods and 7 cubes: 57. Add one more cube instead and you have 4 rods and 8 cubes: 48.
Watch the tricky crossings
- One more than 39 is 40. Nine ones plus one makes a new ten.
- One less than 60 is 59.
- Ten more than 95 is 105. Nine tens plus one ten makes a hundred.
- Ten less than 103 is 93.
Worked examples
Example 1: What is ten more than 47?
The tens digit goes from 4 to 5. Answer: 57.
Example 2: What is one less than 70?
Count back one: 69.
Example 3: Start at 23. Go ten more, then one more. Where do you end?
23 → 33 → 34.
Common mistakes
- Changing the ones digit when asked for ten more. 47 + 10 is not 48.
- Forgetting to cross a ten, like saying one more than 29 is "20-10".
- Mixing up up and down on the hundred chart.
Try it yourself
- One more than 58
- One less than 40
- Ten more than 62
- Ten less than 81
- Ten more than 90
Answers: 1) 59 2) 39 3) 72 4) 71 5) 100
Quick recap
- One more / one less changes the ones digit.
- Ten more / ten less changes the tens digit.
- On a hundred chart, down is +10 and up is −10.