JAMB 1993 · UME · Q26

A regular polygon has $150^\circ$ as the size of each interior angle. How many sides has the polygon?

Worked solution (try it first)

An interior angle and its exterior angle add up to $180^\circ$ , so each exterior angle is $180^\circ - 150^\circ = 30^\circ$ .
The exterior angles add up to $360^\circ$ , so the number of sides is $360 \div 30 = 12$ , option A.