New
New
Year 3

# Add two 3-digit numbers using partitioning

I can add two 3-digit numbers using partitioning.

New
New
Year 3

# Add two 3-digit numbers using partitioning

I can add two 3-digit numbers using partitioning.

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## Lesson details

### Key learning points

1. Partitioning can be used to add 3-digit numbers
2. Unitising means we can use known facts to add larger numbers. For example, 370 + 260 is equal to 37 tens add 26 tens.

### Common misconception

Pupils may not understand that a tens counter has a value of ten. For example, they may think that 14 tens and 11 tens make 25 altogether, forgetting to convert 25 tens into 250.

Encourage counting in tens using counters to begin with. Move onto modelling questions using base ten so the children can count the tens blocks.

### Keywords

• Sum - The sum means the total when the numbers are added together.

• Unitising - Unisiting means treating groups that contain the same number of things as 'ones' or 'units'.

This strategy is shown with practical resources and jottings but the end goal is for the children be able to do it mentally so try to reduce such supports as quickly as possible.
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.
An addend is a number multiplied by a number.
An addend is a number subtracted from another.
Q2.
What should you add to 70 to make 100?
Correct Answer: 30, thirty, Thirty, 3 tens, three tens
Q3.
What would you add to 92 to make 100?
Correct Answer: 8, eight, Eight, 8 ones, eight ones
Q4.
92 + 14 =
Correct Answer: 106, one-hundred and six, one hundred and six, One hundred and six, One-hundred and six
Q5.
= 107 − 9
Correct Answer: 98, Ninety-eight, ninety-eight, Ninety eight, ninety eight
Q6.
The bucket balance has been filled with marbles and blocks. It is balanced. Which of these most closely represent the equation shown by the bucket balance?
2 + 2 = 2 + 2
2 + 3 = 2 + 3
Correct answer: 2 + 3 = 4 + 1
Correct answer: 3 + 2 = 1 + 4
3 + 3 = 2 + 4

## Exit quiz

### 6 Questions

Q1.
Which group has a different number of 'units'?
Q2.
Match the units with their value.

30

300

3

40

500

7

Q3.
Match the expressions.
Correct Answer:4 + 5,4 ones + 5 ones

4 ones + 5 ones

Correct Answer:4 tens + 5 tens,40 + 50

40 + 50

Correct Answer:4 hundreds + 5 hundreds,400 + 500

400 + 500

Correct Answer:32 + 54,32 ones + 54 ones

32 ones + 54 ones

Correct Answer:32 tens + 54 tens,320 + 540

320 + 540

Correct Answer:450 + 390,45 tens + 39 tens

45 tens + 39 tens

Q4.
130 + 150 =
Correct Answer: 280, two hundred and eighty, 28 tens
Q5.
Match the expressions with the most relevant strategy for mental addition.