WAEC 2021 · Paper 1 · Q14

In the diagram, $\angle ABC$ and $\angle BCD$ are right angles, $\angle BAD = t$ and $\angle EDF = 70^\circ$ . Find the value of $t$ .

Worked solution (try it first)

$ADF$ and $CDE$ are straight lines, so $\angle ADC = \angle EDF = 70^\circ$ (vertically opposite).
$AB$ and $CD$ are both perpendicular to $BC$ , so $AB \parallel CD$ .
So $t$ and $\angle ADC$ are co-interior: $t = 180^\circ - 70^\circ = 110^\circ$ , option D.