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Australia
Year 3

6.01 Repeated addition

Lesson

Are you ready?

Let's try this problem to help us remember how to double a number.

Examples

Example 1

Double 9.

Worked Solution
Create a strategy

"Double" means "multiply by 2."

Apply the idea

We can think of 9\times 2 as 2 groups of 9 just like in the image below:

The image shows 2 rows of 9 squares.

Count the number of squares to get:

9\times 2 =18

Idea summary

To double a number, we multiply the number by 2.

Repeated addition

When we add the same number more than once, we can think of it as multiplication, as we see in this video.

Loading video...

Examples

Example 2

Write this addition as a multiplication. 4+4+4+4

Worked Solution
Create a strategy

We can rewrite the addition as a multiplication using: \text{Number of groups}\times\text{Amount in each group}.

Apply the idea

We have 4 groups of 4. We can rewrite this as multiplication: 4+4+4+4=4\times 4

Idea summary

If we are adding groups of the same size, we can also write it as a multiplication:

\text{Number of groups}\times\text{Amount in each group}

Outcomes

AC9M3A02

extend and apply knowledge of addition and subtraction facts to 20 to develop efficient mental strategies for computation with larger numbers without a calculator

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