How fast is the river flowing?

Question

A boat takes 2.70 hours to travel 35.0 km down a river, then 5.90 hours to return. How fast is the river flowing?

Answer 1

This is a math problem and you may use algebra to solve it.
Let the boat speed in the still water to be x and the river flowing speed to be y. We have:
35.0/(x + y) = 2.70
35.0/(x - y) = 5.90
You get the answer immediately by solving these two simultaneous equations.