# 3.02 Groups and arrays

Lesson

## Ideas

Do you remember how multiplication can be thought of as  repeated addition  ?

### Examples

#### Example 1

a

Write this addition as a multiplication:\,\, 10+10+10+10+10+10+10+10

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 8 groups of 10. We can rewrite this as multiplication: 10+10+10+10+10+10+10+10=8\times 10

b

Find the value of 8 \times 10.

Worked Solution
Create a strategy

Use skip counting or a multiplication table.

Apply the idea

By skip counting by 10 eight times, we have10, \,20, \,30, \,40, \,60, \,70, \,80

So, 8 \times 10=80.

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}

## Arrays as products

In this video we see how rows and columns (called an array), can be used to solve multiplication.

### Examples

#### Example 2

Which of these number sentences describe the array?

There may be more than one correct answer.

A
8 \times 2 =16
B
16 \times 2 = 8
C
2 \times 8 =16
Worked Solution
Create a strategy

If we multiply the number of rows by the number of columns, we find the total number of squares.

Apply the idea

The number sentences which describe the array are options A and C.

Idea summary

We get the same answer whichever way we look at our array.

### Outcomes

#### MA2-6NA

uses mental and informal written strategies for multiplication and division