Choose exam board for KS4 Computer Science (GCSE)
Choose exam board for KS4 English
Choose exam board for KS4 French
Choose exam board for KS4 Geography
Choose exam board for KS4 German
Choose exam board for KS4 History
Choose tier for KS4 Maths
Choose exam board for KS4 Music
Choose exam board for KS4 Physical education (GCSE)
Choose exam board for KS4 Religious education (GCSE)
Choose exam board for KS4 Spanish

      Calculating missing side lengths from the area of composite rectilinear shapes

      Lesson details

      Learning outcome

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

      Key learning points

      1. Given the area, it is possible to calculate a missing side length.
      2. 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.

      Teacher tip

      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.

      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

      Loading...

      Prior knowledge starter quiz

      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$$^2$$

      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

      To help you plan your 7 maths lesson on: Calculating missing side lengths from the area of composite rectilinear shapes, download all teaching resources for free and adapt to suit your pupils' needs...