New
New
Year 4

Solve problems involving the perimeter and side lengths of polygons

I can use knowledge of side lengths and perimeter to solve problems.

New
New
Year 4

Solve problems involving the perimeter and side lengths of polygons

I can use knowledge of side lengths and perimeter to solve problems.

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Lesson details

Key learning points

  1. Perimeter is the sum of the side lengths of a 2D shape.
  2. Mental and written methods can be used to calculate the perimeter of a 2D shape.
  3. Combinations of addition, subtraction, multiplication and division can be used to solve problems involving perimeter.

Keywords

  • Perimeter - The distance around a two-dimensional shape.

  • Regular - A regular polygon has all sides equal and all angles equal.

Common misconception

Pupils may think that if they know the perimeter of a shape, and a new shape has been made from duplicates of it, they can simply multiply the perimeter by how many shapes make up the new one.

The lesson highlights this misconception and tackles it but it is worth being aware of it as pupils work. Point out to them that some of the sides from the original shape are now inside the new shapes so do not count as part of its perimeter.

This lesson has been presented pictorially but if you have access to physical regular shapes, you could redesign the lesson based around these to provide pupils with a memorable hands-on problem solving experience.
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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6 Questions

Q1.
Continue the sequence: 3, 6, 9, 12,
Correct Answer: 15
Q2.
Which of these numbers would you say if you were counting in fours from zero?
14
Correct answer: 16
22
Correct answer: 48
Q3.
Match the number of sides to the shape name.
Correct Answer:3 equal sides ,regular triangle

regular triangle

Correct Answer:4 equal sides , square

square

Correct Answer:5 equal sides ,regular pentagon

regular pentagon

Correct Answer:6 equal sides ,regular hexagon

regular hexagon

Q4.
What is the side length of a square with a perimeter of 20 cm?
4 cm
Correct answer: 5 cm
10 cm
80 cm
Q5.
What is the side length of a regular triangle with a perimeter of 30 cm? cm
Correct Answer: 10
Q6.
What is the side length of a regular five-sided polygon with a perimeter of 25 cm? cm.
Correct Answer: 5

6 Questions

Q1.
A regular triangle and a square have the same perimeter, which is a whole number. What could the perimeters be?
6
8
Correct answer: 12
15
Q2.
A regular triangle and a square each have a perimeter of 12 cm. What is the side length of each shape?
The triangle has a side length of 3 cm.
Correct answer: The triangle has a side length of 4 cm.
Correct answer: The square has a side length of 3 cm.
The square has a side length of 4 cm.
Q3.
Shape A is a square with a perimeter of 16 cm. A new shape has been composed from copies of shape A. What is its perimeter? cm.
An image in a quiz
Correct Answer: 32
Q4.
Shape A is a square with a perimeter of 16 cm. A new shape has been composed from copies of shape A. What is its perimeter? cm.
An image in a quiz
Correct Answer: 32
Q5.
Shape A is a square with a perimeter of 12 cm. A new shape has been composed from copies of shape A. What is its perimeter? cm.
An image in a quiz
Correct Answer: 30
Q6.
Shape A is a regular hexagon with a perimeter of 30 cm. A new shape has been composed from copies of shape A. What is its perimeter? cm.
An image in a quiz
Correct Answer: 60