# Add and subtract 1 to and from a 2-digit number crossing the tens boundary

I can add and subtract one to and from a two-digit number crossing the tens boundary.

# Add and subtract 1 to and from a 2-digit number crossing the tens boundary

I can add and subtract one to and from a two-digit number crossing the tens boundary.

## Lesson details

### Key learning points

- Finding one more is the same as adding one; finding one less is the same as subtracting one.
- Numbers that are one more or one less than each other have a difference of one.
- When one is added to a number with a ones digit of 9, the next multiple of ten will be reached.
- When one is subtracted from a multiple of ten, the number reached will have a ones digit of 9
- When one ten is changed for ten ones, or ten ones for one ten, it is called regrouping.

### Common misconception

Children may have difficulty finding one less than a multiple of ten saying, for example, one less than 60 is 69.

Refer to the order of the decades counting forwards and backwards and encourage visualisation of the decades on number lines and one hundred squares to support this. Help children to generalise about the number before a decade number ending in 9

### Keywords

One more - One more is when there is a greater amount by one or another item in the set.

One less - One less is when there is a smaller value by one.

Difference - The result of subtracting one number from another, How much one number differs from another.

Decade - A group of ten numbers below one hundred, each with the same tens digit.

Regroup - To exchange ten ones for one ten or one ten for ten ones in order to calculate more easily.

### Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

## Video

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## Starter quiz

### 6 Questions

35

33

35