JAMB 2017 · UTME (set 2) · Q39

In a regular polygon, each interior angle is double its corresponding exterior angle. Find the number of sides of the polygon.

Worked solution (try it first)

Let the exterior angle be $e$ .
The interior angle is $2e$ , and the two add up to $180^\circ$ : $3e = 180^\circ$ , so $e = 60^\circ$ .
The exterior angles add up to $360^\circ$ , so the number of sides is $360 \div 60 = 6$ , option B.