# 7.02 Perimeter

Lesson

## Ideas

Can you  add multiple numbers  together?

### Examples

#### Example 1

Solve 40 + 20 + 3.

Worked Solution
Create a strategy

Use a number line.

Apply the idea

Plot the first number on the number line:

Then jump forward by 20 to get 60:

Then jump forward by 3 to get 63:

40+20+3=63

Idea summary

When adding numbers we can use a number line or add digits by place value.

## Perimeter using unit squares

The perimeter of a shape is the length around the outside of the shape.

If a shape is made up of unit squares, we can use those to count the distance around the outside of the whole shape. We count the outside edges of every unit square, making sure we include the whole outside of our shape.

### Examples

#### Example 2

Find the perimeter of the shaded region shown, where each square has a length of 1 unit.

Worked Solution
Create a strategy

We can count the unit edges outside the shaded shape.

Apply the idea

The shape has 10 unit edges around it.

Perimeter =10 units

Idea summary

To find the perimeter we count the edge of every unit square, around the outside of our shape.

## Perimeter

2D shapes are also known as polygons, and we've seen some of these shapes before. This video looks at how to work out the perimeter of any polygon.

### Examples

#### Example 3

Find the perimeter of the figure shown.

Worked Solution
Create a strategy

Add all the lengths of the sides to find the perimeter.

Apply the idea
Idea summary

It doesn't matter what shape our polygon is, as long as we add the length of every side, we can work out the perimeter.

We must also write the unit of measurement with our answers, such as \text{cm, m, mm}, or \text{km}.

### Outcomes

#### MA3-9MG

selects and uses the appropriate unit and device to measure lengths and distances, calculates perimeters, and converts between units of length