posted by Sarah .
The current river flows at rate of 4mph. In order for a boat to travel 24 miles up river and then return in a total of 5 hours how fast must the boat be able to travel in still water?
if the boat's speed is s mi/hr, then since time=distance/speed, we have
24/(s-4) + 24/(s+4) = 5
s = 11.05