JAMB 2004 · UME · Q24

The sum of the interior angles of a pentagon is $6x + 6y$ . Find $y$ in terms of $x$ .

Worked solution (try it first)

The interior angles of a pentagon add up to $(5 - 2) \times 180^\circ = 540^\circ$ , so $6x + 6y = 540$ .
Divide by 6: $x + y = 90$ .
Subtract $x$ : $y = 90 - x$ , option B.