3. Multiplication strategies

3.01 Repeated addition as multiplication

3.02 Groups and arrays

PRACTICE: x2,4,8

PRACTICE: Multiplication

3.10 Multiply and divide by 10; the powers of 10

Year 4

3.05 x3

Lesson

Ideas

Are you ready?
Multiply numbers by 3

Are you ready?

Can you write repeated addition as a multiplication number sentence?

Examples

Example 1

Write this addition as a multiplication.

2 +2 +2

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 3 groups of 2. We can rewrite this as multiplications: 2+2+2 = 3\times 2

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}

Multiply numbers by 3

Let's look at how to multiply numbers by 3.

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Examples

Example 2

Find the product of 3\times 6.

Worked Solution

Create a strategy

We can think of 3 \times 6 as 3 groups of 6. The image shows 3 groups of 6 squares:

The image shows 3 rows of 6 squares.

Apply the idea

There are 18 squares in the above image.3 \times 6 = 18

Idea summary

Multiplying by three is the same as tripling. We always multiply equally sized groups.

Outcomes

AC9M4A02

recall and demonstrate proficiency with multiplication facts up to 10 x 10 and related division facts; extend and apply facts to develop efficient mental strategies for computation with larger numbers without a calculator

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