smc

Question

At his usual rate a man rows 15 miles downstream in five hours less time than it takes him to return. If he doubles his usual rate, the time downstream is only one hour less than the time upstream. In miles per hour, the rate of the stream's current is:

Accepted Answer

Let the speed of rowing in still water and water speed be r, w. Then: 15r-w-15r+w=5. 152r-w-152r+w=1. Solving (remember: both variables must be positive!), we have r=4, w=2. Select 2.