Question

If y varies directly as x, and y = 25 when x = 5, find y when x = 25.

Answer 1

It would be 125 so A

Answer 2

$\bf \qquad \qquad \textit{direct proportional variation} \\\\ \textit{\underline{y} varies directly with \underline{x}}\qquad \qquad y=kx\impliedby \begin{array}{llll} k=constant\ of\\ \qquad variation \end{array}\\\\ \rule{31em}{0.25pt}\\\\ \textit{we also know that } \begin{cases} y=25\\ x=5 \end{cases}\implies 25=k5\implies \cfrac{25}{5}=k \\[2em] 5=k\hspace{20em}\boxed{y=5x} \\[2em] \textit{when x = 25, what is \underline{y}?}\qquad y=5(25)\implies y=125$