NECO 2023 · Paper 1 · Q38

An interior angle of a regular polygon is $108^\circ$ . Find the number of sides of the polygon.

Worked solution (try it first)

An interior angle and its exterior angle add up to $180^\circ$ , so each exterior angle is $180^\circ - 108^\circ = 72^\circ$ .
The exterior angles add up to $360^\circ$ , so the number of sides is $360 \div 72 = 5$ , option B.