Question

two quantites, x and y, are directly proportional. if x is halved, what happened to y?

Answer 1

If x and y are proportional x halved=y halved

Answer 2

$\bf \qquad \qquad \textit{direct proportional variation} \\\\ \textit{\underline{y} varies directly with \underline{x}}\qquad \qquad y=kx\impliedby \begin{array}{llll} k=constant\ of\\ \qquad variation \end{array} \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ x=\cfrac{x}{2}~\hspace{7em}y=k\cdot \cfrac{x}{2}\implies y=\cfrac{kx}{2}\implies \stackrel{doubled}{\stackrel{\downarrow }{2y}=kx}$