WAEC 2021 · Paper 1 · Q27

Which of the following is not an exterior angle of a regular polygon?

Worked solution (try it first)

The exterior angles of a regular polygon are equal and add up to $360^\circ$ , so an exterior angle must divide $360^\circ$ a whole number of times.
$360 \div 72 = 5$ , $360 \div 24 = 15$ and $360 \div 15 = 24$ : all whole numbers.
$360 \div 66 \approx 5.45$ is not whole, so $66^\circ$ is not an exterior angle, option A.