New
New
Year 3

# Solve problems by adding and subtracting to or from 3-digit numbers

I can solve problems by adding to and subtracting from 3-digit numbers.

New
New
Year 3

# Solve problems by adding and subtracting to or from 3-digit numbers

I can solve problems by adding to and subtracting from 3-digit numbers.

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## Lesson details

### Key learning points

1. Number lines can record the steps in our thinking when we are partitioning to add and subtract.
2. The 1s digit does not change when you add or subtract a multiple of ten.
3. Number facts to 10 help when crossing the 10s and 100s boundaries.

### Common misconception

Pupils may struggle to partition 10s numbers to help them bridge a 100s boundary.

Encourage pupils to calculate the number of tens needed to add or subtract to the 100s number, then add or subtract the remainder.

### Keywords

• Bridge - Bridging is a strategy which uses addition or subtraction to cross a number boundary.

• Partition - Partition means splitting an object or value down into smaller parts.

• 100s boundary - The 100s boundary is the point at which the numbers change into 100s numbers, or from one set of hundreds to another.

Pupils will need to use number lines to represent their thinking. Base ten blocks may also be helpful for some pupils, although these do not feature in the lesson. They can be used alongside number lines to support pupil learning.
Teacher tip

### 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).

## Starter quiz

### 6 Questions

Q1.
How should you partition 5 to calculate 98 + 5?
Q2.
Which calculations cross a 100s boundary?
190 − 30
220 + 30
Q3.
What is 230 + 30?
Q4.
270 − 40 =
Q5.
Which calculation is shown by the number line representation?
397 + 3 = 403
397 + 5 = 403
396 + 6 = 403
Correct answer: 397 + 6 = 403
Q6.
Use the number line to find the missing number. 510 − ___ = 460
10
20
40

## Exit quiz

### 6 Questions

Q1.
How should you partition 60 to calculate 160 + 60?
Q2.
How should you partition 60 to calculate 210 − 60?
Correct answer: subtract 10 then subtract 50
subtract 20 then subtract 40
subtract 30 then subtract 30
Q3.
245 + 20 =
Correct Answer: 265, two hundred and sixty five
Q4.
320 − 40 =
Correct Answer: 280, two hundred and eighty
Q5.
Colin the cat is 410 cm high in a tree. He climbs down 50 cm. How high is he now?
350 cm