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Year 7

Perimeter with composite rectilinear shapes

You can use the properties of a range of polygons to deduce the perimeters of compound shapes, including generalising a perimeter formula where appropriate.

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Year 7

Perimeter with composite rectilinear shapes

You can use the properties of a range of polygons to deduce the perimeters of compound shapes, including generalising a perimeter formula where appropriate.

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Share activities with pupils
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Lesson details

Key learning points

  1. You can identify how to find the perimeter of compound shapes made of rectangles.
  2. You can calculate the perimeter of compound shapes made from rectangles.
  3. You can generalise the perimeter of compound shapes made of rectangles.
  4. It is possible to find missing lengths in compound shapes made from rectangles.

Keywords

  • Compound shape - A compound shape is a shape created using two or more basic shapes.

  • Composite shape - A composite shape is an alternative term for a compound shape.

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

Common misconception

Pupils may think they can always double the length and width to calculate the perimeter.

This only works for composite rectilinear shapes if the lengths do not overlap.

Pupils may benefit from using manipulatives here. Consider using strands of uncooked spaghetti which can be used to make a composite rectilinear shape and then moved to create a rectangle.
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).

Lesson video

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Starter quiz

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6 Questions

Q1.
What is the length of the side marked $$a$$ in the diagram?
An image in a quiz
Correct Answer: 2 cm, 2 centimeters, two centimeters, two cm
Q2.
What is the length of the side marked $$b$$ in the diagram?
An image in a quiz
Correct Answer: 4 cm, 4 centimeters, four centimeters, four cm
Q3.
Mariam wants to fence in a pentagonal garden. Each side of the pentagon measures 6 meters. What is the perimeter of Mariam's garden?
6 m
24 m
Correct answer: 30 m
36 m
Q4.
Mia wants to enclose her garden in the shape of an irregular hexagon. The lengths of the sides of the hexagon are 5 m, 7 m, 4 m, 6 m, 9 m, and 8 m. What is the perimeter of Emma's garden?
Correct Answer: 39 m, 39 meters, thirty-nine meters, thirty nine meters, 39 meters
Q5.
Alex wants to frame a triangular picture. The lengths of two sides of the triangle are 80 cm and 120 cm. If the perimeter of the triangle is 350 meters, what is the length of the third side?
Correct Answer: 150 cm, 150 centimeters, One hundred and fifty cm
Q6.
Jun wants to build a rectangular pond in his backyard. The pond has a length of 2.6 m and a perimeter of 8.6 meters. What is the width of the pond?
Correct Answer: 1.7 m, 1.7 meters

Exit quiz

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6 Questions

Q1.
True or false? A composite shape is an alternative term for a compound shape.
Correct answer: True
False
Q2.
Calculate the perimeter of the shape.
An image in a quiz
24 cm
Correct answer: 30 cm
39 cm
48 cm
Q3.
A shape is a shape created using two or more basic shapes.
Correct Answer: compound, composite
Q4.
A composite rectilinear shape is made from ______
triangles
quadrilaterals
Correct answer: rectangles
polygons
Q5.
Calculate the perimeter.
An image in a quiz
Correct Answer: 21.2 m, 21.2 meters
Q6.
Calculate the perimeter.
An image in a quiz
Correct Answer: 118 units, 118