# 7.03 Perimeter of rectangles

Lesson

## Ideas

If we can add three or more numbers together, that can help us in this lesson. Let's try this problem to practice.

### 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 of rectangles

This video looks at using the properties of rectangles to calculate the perimeter, it also talks about some special notation that is often used to show when two sides have the same length.

### Examples

#### Example 2

Find the perimeter of the rectangle shown.

Worked Solution
Create a strategy

We can use the formula for a rectangle: \text{Perimeter}=2 \times (\text{Length} + \text{Width} ).

Apply the idea

First add the length and width:

Now multiply this by 2 to get the perimeter:

Idea summary

Because a rectangle has 2 pairs of sides with equal length, we can add the length and width, then double it, to find the perimeter of a rectangle.

A square is a special kind of rectangle, with 4 sides the same length, so we can multiply its side length by 4.

### Outcomes

#### MA3-9MG

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