[tex]\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}\\\\
-------------------------------\\\\
\textit{\underline{time} varies directly with \underline{distance}}\qquad t=kd
\\\\\\
\textit{we also know that }
\begin{cases}
t=\stackrel{seconds}{10}\\
d=\stackrel{miles}{2}
\end{cases}\implies 10=k2\implies \cfrac{10}{2}=k[/tex]
and surely you know how much that is.
