# Find the number of sides when given the sum of interior angles

## Lesson details

### Key learning points

1. In this lesson, we will find the number of sides of a polygon when given only the sum of interior angles.

### Licence

This content is made available by Oak National Academy Limited and its partners and licensed under Oak’s terms & conditions (Collection 1), except where otherwise stated.

## Video

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## Worksheet

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## Starter quiz

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### 4 Questions

Q1.
What is the sum of interior angles of a 20-sided shape?
1800º
2880º
3600º
Q2.
What is the sum of interior angles of a 9-sided shape?
1620º
1980º
900º
Q3.
What is the missing angle, labelled x?
114º
33º
Q4.
What is the size of each interior angle in a regular octagon?
225º
45º
90º

## Exit quiz

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### 4 Questions

Q1.
The sum of interior angles of a polygon is 720º. How many sides does the polygon have?
5
7
8
Q2.
The sum of interior angles of a polygon is 2880º. How many sides does the polygon have?
15
16
17
Q3.
The sum of interior angles of a regular polygon is 3960º. What is the size of each interior angle of the regular polygon?
150º
170º
175º
Q4.
The sum of interior angles of a regular polygon is 5040º. What is the size of each exterior angle of the regular polygon?
100.8º