Answer
$k=.25$, $y=.25x$
Work Step by Step
If y varies directly as x, we know that the variables x and y can be related by the function $y=kx$, where k is the constant of proportionality.
If $y=.2$ when $x=.8$, then we know that $.2=.8k$ (or $\frac{1}{5}=\frac{4}{5}k$). Multiply both sides by 5.
$4k=1$
Divide both sides by 4.
$k=\frac{1}{4}=.25$
Therefore, the constant of variation is $k=.25$ and the direct variation equation is $y=.25x$.
