Solve the problem.
-A boat heads upstream a distance of 30 miles on the Mississippi river, whose current is running at 5 milesper hour. If the trip back takes an hour less, what was the speed of the boat in still water? Give the answerrounded to two decimal places, if necessary.
A)18.03 mph
B)16.58 mph
C)6 mph
D)15 mph

Question

Quizplus · Accepted Answer

The speed of the boat in still water is 18.03 mph. This is found by setting up equations based on the distance formula $d = rt$, where $d$ is distance, $r$ is rate, and $t$ is time. Let $x$ be the speed of the boat in still water. The upstream trip takes $\frac{30}{x-5}$ hours, and the downstream trip takes $\frac{30}{x+5}$ hours. The downstream trip takes 1 hour less, so $\frac{30}{x-5} - \frac{30}{x+5} = 1$. Solving this equation for $x$ gives the speed of the boat in still water as approximately 18.03 mph.

Solve the Problem. -A Boat Heads Upstream a Distance of 30 Miles on 30