JAMB 2014 · UTME · Q16

$P$ varies directly as $Q$ and inversely as $R$ . When $Q = 36$ and $R = 16$ , $P = 27$ . Find the relation between $P$ , $Q$ and $R$ .

Worked solution (try it first)

Directly as $Q$ (on top), inversely as $R$ (underneath): $P = \dfrac{kQ}{R}$ .
Put in the values: $27 = \dfrac{36k}{16}$ , so $k = \dfrac{27 \times 16}{36} = 12$ .
So $P = \dfrac{12Q}{R}$ , option C.