Reason about compound shapes using the relationship between side lengths and area and perimeter

I can reason about compound shapes using the relationship between side lengths and area and perimeter.

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Year 6

Reason about compound shapes using the relationship between side lengths and area and perimeter

I can reason about compound shapes using the relationship between side lengths and area and perimeter.

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Share activities with pupils

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Lesson details

Key learning points

Area and perimeter are calculated from the side lengths of 2D shapes.
Area and perimeter are measured in different units.
Compound shapes can be decomposed and rearranged in different ways.

Keywords

Compound - A compound shape is a shape created using two or more basic shapes.
Dimension - A dimension is a measurement of length in one direction.

Common misconception

The numbers used as side lengths in this lesson are generally relatively low, and based around times tables. As a result, pupils might be tempted to guess / estimate the missing side lengths.

Remind pupils that the shapes are not to scale and encourage them to use subtraction skills instead - what is the difference between this known side length and this known side length?

Physically cutting out the compound shapes and decomposing them that way, rather than drawing a line inside them, provides a powerful reminder that compound shapes are composed of two or more shapes. Manipulating the shapes will help to show how the missing side lengths can be calculated.

Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).