College Algebra, Exercise P, Exercise P.4, Section Exercise P.4, Problem 100

The speed of light is about 186,000 $\displaystyle \frac{\text{mi}}{\text{s}}$ and the distance from the earth to the sun is about 93 million miles. Find how long it takes for a light ray from the sun to reach the Earth.

Recall that velocity $\displaystyle V = \frac{d}{t}$, where $d$ is the distance from the Earth to the Sun and $V$ is the speed of light.
Solve for $t$

$
\begin{equation}
\begin{aligned}
V &= \frac{d}{t}\\
\\
t &= \frac{d}{V} && \text{Model}\\
\\
t &= \frac{93,000,000 \cancel{\text{mi}} }{186,000 \frac{\cancel{\text{mi}}}{sec}} && \text{Change to scientific notation}\\
\\
t &= \frac{9.3 \times 10^7}{1.86 \times 10^5} \text{sec} && \text{Group}\\
\\
t &= \frac{9.3}{1.86} \times 10^{7-5} \text{sec} && \text{Simplify}\\
\\
t &= 5 \times 10 ^2 \text{sec} && \text{Simplify}\\
\\
t &= 500 \text{sec}
\end{aligned}
\end{equation}
$


It will take 500 sec for a light ray from the sun to reach the Earth.