JAMB 2013 · UTME · Q14

Variation

$P$ varies jointly as $m$ and $u$ , and inversely as $q$ . Given that $P = 4$ , $m = 3$ , $u = 2$ and $q = 1$ , find the value of $P$ when $m = 6$ , $u = 4$ and $q = \frac85$ .

Worked solution (try it first)

Jointly as $m$ and $u$ (on top), inversely as $q$ (underneath): $P = \dfrac{kmu}{q}$ .
$P = 4$ , $m = 3$ , $u = 2$ , $q = 1$ : $4 = 6k$ , so $k = \frac23$ .
Now $mu = 24$ , so $P = \frac23 \times 24 \div \frac85$ , which is $16 \times \frac58 = 10$ , option A.

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