Question

The number of hours needed to complete a trip, h, varies inversely with drivingspeed, d. A trip can be completed in 5 hours at a speed of 60 miles per hour. Howmany hours would it take to complete the trip at a speed of 75 miles per hour?

Answer 1

If h varies inversely to s, then we can use the next equation:

$h=\frac{k}{s}$

Then, when s= 60 and h=5.

Replacing:

$5=\frac{k}{60}$

Solve for k:

$\begin{gathered} k=5\ast60 \\ k=300 \end{gathered}$

Now, if s=75 and k=300:

$\begin{gathered} h=\frac{300}{75} \\ h=4 \end{gathered}$

Hence, it will take 4 hours.