It takes a boat 3 hours to travel down a river from point A to point B, and 5 hours to travel up the river from B to A. How long would it take the same boat to go from A to B in still water?  Choose the correct answer.
A) 3 hours and 45 minutes. B) 2 hours and 32 minutes. C) 4 hours and 54 minutes. D) 6 hours and 26 minutes. E) 5 hours and 59 minutes.
Let: S be the speed of the boat in still water, r be the rate of the water current and d the distance between A and B.   d = 3(S + r) : boat traveling down river   d = 5(S - r) : boat traveling up river   3(S + r) = 5(S - r)   r = S / 4 : solve above equation for r   d = 3(S + S/4) : substitute r by S/4 in equation B   d / S = 3.75 hours = 3 hours and 45 minutes.   correct answer 3 hours and 45 minutes.
<result>A</result>
It takes a boat 3 hours to travel down a river from point A to point B, and 5 hours to travel up the river from B to A. How long would it take the same boat to go from A to B in still water?