Lesson

Comparing objects with different areas will help us to estimate in this lesson. Let's try a problem to review.

Look at the two shapes on the grid.

a

What are the areas of Shape A and Shape B?

Worked Solution

b

Which is the smallest shape?

Worked Solution

Idea summary

We can easily compare the area of shapes if their units are the same. In that case we just compare the numbers.

When we have a 2D shape, the amount of space it takes up is the area of that shape. Choosing the appropriate unit of measurement can mean things make more sense, so let's see how to do this in the video.

It is most appropriate to use square metres \left(\text{m$^2$}\right) to measure the area of:

A

Your classroom

B

An exercise book

C

A matchbox

D

Australia

Worked Solution

Idea summary

We can use some measurements of length from smallest to biggest: \text{mm$^2$}, \text{cm$^2$}, \text{m$^2$}, \text{km$^2$}.

This video looks at how to use what you know about size and space to estimate area.

What is the most appropriate estimate for the area of a postage stamp?

A

5 \text{ cm}^2

B

3 \text{ m}^2

C

5 \text{ km}^2

Worked Solution

Idea summary

Sometimes, it might be that two different units of measurement are appropriate. In that case, you can choose which one to use. The area of some insects, for example, could be measured with \text{mm$^2$} or \text{cm$^2$}.

A good strategy when estimating the area is to think about the area of things we know. This helps us determine if things make sense, or not.