Thinking Mathematically (6th Edition)

Substitute $245$ for $L$ in the given formula and calculate $v$. That is., Write $245$ into its prime factors and take square root. That is., $v=2\sqrt{5L}$ $v=2\sqrt{5*245}$ \begin{align} & v=2\sqrt{5\times 5\times {{7}^{2}}} \\ & =2\times 5\times 7 \\ & =70 \end{align} Thus, the speed of motorist was $70\text{ mph}$. Since it is greater than $50\text{ mph}$, he was speeding.