Question

The graph of a proportional relationship passes through (6, 42) and (1, y). Find y.

Answer 1

well, another way to word it will be, we know "x" and "y" are directly proportional, we also know that x = 6 when y = 42, what is "y" when x = 1?

$\bf \qquad \qquad \textit{direct proportional variation} \\\\ \textit{\underline{y} varies directly with \underline{x}}\qquad \qquad \stackrel{\textit{constant of variation}}{y=\stackrel{\downarrow }{k}x~\hfill } \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ \textit{we know that } \begin{cases} x = 6\\ y =42 \end{cases}\implies 42 = k(6)\implies \cfrac{42}{6}=k\implies 7=k \\\\\\ \textit{therefore}\qquad \qquad \boxed{y = 7x} \\\\\\ \textit{when x = 1, what is \underline{y}?}\qquad y = 7(1)\implies y = 7$