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Year 4

Calculate the side length of a regular polygon by division where the perimeter is known

I can use division to calculate the side length of a regular polygon when the perimeter is known.

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New
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Year 4

Calculate the side length of a regular polygon by division where the perimeter is known

I can use division to calculate the side length of a regular polygon when the perimeter is known.

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Lesson details

Key learning points

  1. If you know the perimeter of a regular polygon you can calculate the length of one side.
  2. Divide the perimeter by the number of sides to calculate the length of one side.
  3. Knowledge of times tables and related division facts can support calculation.

Keywords

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

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

Common misconception

Pupils often find division a trickier concept than multiplication and do not connect this to their known multiplication facts.

Establish the inverse relationship with multiplication and show how the division equations can be re-written as a multiplication equation with a missing factor. Support pupils in making this connection to allow them to use known facts to calculate.

Known multiplication facts are key in this lesson and pupils should be increasingly fluent in tables learned in Years 2 and 3. Multiplication grids may be a useful scaffold for less confident pupils.
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.
Select all of the squares.
Correct answer: a
Correct answer: b
c
d
Q2.
What is the perimeter of a square with a side length of 5 cm? cm.
Correct Answer: 20
Q3.
What is the perimeter of a regular triangle with a side length of 5 cm? cm.
Correct Answer: 15
Q4.
What is the perimeter of a regular pentagon with a side length of 5 cm? cm.
Correct Answer: 25, 25 cm
Q5.
Lucas is trying to work out 20 ÷ 5 but he is struggling. How else might he think of this question?
5 + _ = 20
Correct answer: _ × 5 = 20
Correct answer: 5 × _= 20
20 − 5 = _
Q6.
Order these shapes from smallest perimeter to longest.
1 - A regular triangle with a side length of 5 cm
2 - A square with a side length of 4 cm
3 - A regular pentagon with a side length of 4 cm

Exit quiz

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6 Questions

Q1.
If you know the perimeter of a regular polygon, what can you do to find the length of each side?
Divide the number of sides by the perimeter.
Correct answer: Divide the perimeter by the number of sides.
Nothing. It is not possible.
Q2.
What is the side length of a square with a perimeter of 16 cm?
2 cm
Correct answer: 4 cm
8 cm
64 cm
Q3.
Lucas has measured the perimeter of his classroom, which is square-shaped. Its perimeter is 24 metres. What is the length of one side of the classroom? m.
Correct Answer: 6 , six
Q4.
What is the side length of a regular triangle with a perimeter of 15 cm? cm.
Correct Answer: 5, five
Q5.
What is the side length of a regular five-sided shape with a perimeter of 30 cm? cm
Correct Answer: 6, six
Q6.
What is the side length of a regular five-sided shape with a perimeter of 300 cm? cm.
Correct Answer: 60