Question

A small motor boat travels to a point five miles upstream and back again in a total time of 1 hour and 20 minutes. If the boat makes 8 miles per hour in still water, what was the velocity of the stream?

Answer 1

speed upstream = 8 - u
speed downstream = 8 + u

time upstream = 5/(8-u)
time downstream =5/(8+u)

so
5(8-u) + 5/(8+u) = (4/3) hr

5(8+u) + 5(8-u) = (4/3)(64-u^2)

15(8+u) + 15(8-u) = 256(64-u^2)

etc, solve quadratic