The speed of a stream is $6 \mathrm{mph}$. If a boat travels 54 miles downstream in the same time that it takes to travel 27 miles upstream, what is the speed of the boat in still water?
A) $18 \mathrm{mph}$
B) $20 \mathrm{mph}$
C) $12 \mathrm{mph}$
D) $21 \mathrm{mph}$

Question

Quizplus · Accepted Answer

The speed of the boat in still water is $x$. Downstream speed is $x + 6$ and upstream speed is $x - 6$. The time taken for both journeys is the same, so $\frac{54}{x+6} = \frac{27}{x-6}$. Solving this equation gives $x = 18$.

The Speed of a Stream Is 6mph6 \mathrm{mph}6mph If a Boat Travels 54 Miles Downstream in the a Boat

The Speed of a Stream Is $6 \mathrm{mph}$ If a Boat Travels 54 Miles Downstream in the a Boat