# 3.04 x8

Lesson

## Ideas

Multiplication looks at equally sized groups.  Doubling  means multiplying equally sized groups by 2. Let's try this problem to remember how.

### Examples

#### Example 1

Find the value of 9\times2.

Worked Solution
Create a strategy

Remember 9 \times 2 is the same as 2 \times 9. This can be thought of as 2 groups of 9.

The picture below shows 2 groups of 9 stars.

Apply the idea

In the above image there are 18 stars altogether.

Idea summary

Multiplying by two is the same as doubling and can be thought of as the total of two equally sized groups.

## Multiply numbers by 8

4 groups is twice (two times) as many as 2 groups. 8 groups is twice (two times) as many as 4 groups. Let's look at how to multiply numbers by 8 using a Double, Double, Double strategy.

### Examples

#### Example 2

Find the value of 8 \times 5.

Worked Solution
Create a strategy

This can be thought of as 8 groups of 5 squares, as represented in the image below.

Apply the idea

There are 40 squares in the above image.8 \times 5 = 40

Reflect and check

Or we can use the double, double, double strategy on 5 to get:

Which means: 8 \times 5 = 40

Idea summary

You can use the Double, Double, Double strategy to multiply a number by 8. To do this, double the number, double the answer, then double the answer again.

### Outcomes

#### MA2-6NA

uses mental and informal written strategies for multiplication and division