MaTh
posted by mo on .
Debbie traveled by boat 5miles upstream to fish in her favourite spot> Because of the 4mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water ????
Please help !!!!!!!!!!!!!!

Let V be the speed in still water, in mph. The speed with respect to land will be V4 upstream and V+4 downstream.
Upstream travel time (in hours) = Downstream travel time + 1/3 hour.
5/(V5)  5/(V+5) = 1/3
Solve for V
[5(V+5)  5(V5)]/(V^2 25) = 1/3
50/(V^225) = 1/3
150 = V^2 25
V = sqrt 175 = 13.23 mph