Topics
6. Multiplication and division
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AustraliaNSW
Stage 2

6.07 Multiplication by 4

Lesson
Practice
Lesson

Are you ready?

Multiplication looks at equally sized groups. Doubling means multiplying equally sized  groups by  2. Can you solve this problem?

Examples

Example 1

Find 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 stars.

The image shows 2 circles with 9 stars each inside.
Apply the idea

In the above image there are 18 stars altogether.

\displaystyle 9\times2\displaystyle =\displaystyle 18
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 4

4 groups is twice (two times) as many as 2 groups. Let's look at how to multiply numbers by 4.

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Examples

Example 2

Find the product of 4\times 4.

Worked Solution
Create a strategy

This can be thought of as 4 groups of 4 squares as shown below.

The image shows 4 rows of 4 squares.
Apply the idea

In the above image there are 16 squares in total.4 \times 4 = 16

Reflect and check

We could also use the Double, Double strategy:

\displaystyle 2\times 4\displaystyle =\displaystyle 8Double 4
\displaystyle 2\times 8\displaystyle =\displaystyle 16Double the answer
Idea summary

To solve questions with 4 times tables, you can use the Double, Double strategy. That means you double the number, then double the answer.

Outcomes

MA2-6NA

uses mental and informal written strategies for multiplication and division

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