A motorboat travels upstream in five hours and makes the ret

A motorboat travels upstream in five hours and makes the return trip downstream in three hours. If the rate of the stream\'s current is ten kilometers per hour, find the rate of the boat in still water.

Solution

Let the distance traveled be D and the rate in still water be R.
The effective rate going upstream is R-10 and downstream is R+10.
The distance traveled is the \"effective\" rate multiplied by the time traveled so:
D = (R-10)*5 going upstream and
D = (R+10)*3 going downsteam
We have then (R-10)*5 = (R+10)*3
Solve for R to get the rate in still water.