Skip to content

New

New

Calculating missing side lengths from the area of composite rectilinear shapes

I can calculate a missing side length from the area of a composite rectilinear shape.

Download all

Lesson 9 of 12

New

New

Year 7

Calculating missing side lengths from the area of composite rectilinear shapes

I can calculate a missing side length from the area of a composite rectilinear shape.

Download all

Lesson slides

Download lesson slides

Skip lesson slides

Lesson details

Key learning points

Given the area, it is possible to calculate a missing side length.
The most efficient method may depend on the features of the shape.

Keywords

Composite rectilinear shape - A composite rectilinear shape is a composite shape made from rectangles.

Common misconception

Pupils may try to combine lengths that are not parallel to a known side length.

For two sets of side lengths to be equal, one set must be parallel to the other and none of the lengths can overlap.

This lesson demonstrates why it is important to have more than one strategy for calculating the area of composite rectilinear shapes. Highlighting this to pupils helps them to understand why one method is not always enough.

Teacher tip

Equipment

Licence

This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

Skip lesson video

Loading...

Worksheet

Download worksheet

Prior knowledge starter quiz

Download quiz pdf

6 Questions

Q1.
Calculate the area of this compound rectilinear shape (you do not need to state the units).

An image in a quiz

Correct Answer: 54, 54 cm$$^2$$

Q2.
Calculate the area of this compound rectilinear shape (you do not need to state the units).

An image in a quiz

Correct Answer: 48, 48 cm$$^2$$

Q3.
Calculate the area of this compound rectilinear shape (you do not need to state the units).

An image in a quiz

Correct Answer: 100, 100 m$$^2$$

Q4.
Calculate the area of this compound rectilinear shape (you do not need to state the units).

An image in a quiz

Correct Answer: 136, 136 m$$^2$$

Q5.
Determine whether there is enough information to find the perimeter of this shape.

An image in a quiz

There is enough information

Correct answer: There is not enough information

Q6.
Calculate the area of this compound rectilinear shape (you do not need to state the units).

An image in a quiz

Correct Answer: 132, 132 m$$^2$$

Assessment exit quiz

Download quiz pdf

6 Questions

Q1.
Calculate the length of the marked side.

An image in a quiz

Correct Answer: 7, 7 cm, a = 7, a = 7 cm

Q2.
Calculate the length of the marked side.

An image in a quiz

Correct Answer: 10, 10 cm, b = 10, b = 10 cm

Q3.
Calculate the length of the marked side.

An image in a quiz

Correct Answer: 12, 12 m, c = 12, c = 12 m

Q4.
Calculate the length of the marked side.

An image in a quiz

Correct Answer: 6, 6 m, d = 6, d = 6 m

Q5.
Is it possible to determine the perimeter of this shape?

An image in a quiz

Yes

Correct answer: No

Q6.
True or false? This is an example of a composite rectilinear shape.

An image in a quiz

True

Correct answer: False

Lesson appears in

UnitMaths / Perimeter and area

Maths