JAMB 2012 · UTME · Q14

Variation

If $y$ varies directly as $\sqrt n$ and $y = 4$ when $n = 4$ , find $y$ when $n = 1\frac79$ .

Worked solution (try it first)

$y = k\sqrt n$ .
Put in $y = 4$ , $n = 4$ : $4 = 2k$ , so $k = 2$ .
$1\frac79 = \frac{16}{9}$ , so $\sqrt n = \frac43$ .
So $y = 2 \times \frac43 = \frac83$ , option C.

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