I'm normally not bad at word problems. This problem comes from a take home test my instructor gave us Tuesday.

The problem reads:

A boat takes five hours to move upstream against a current of 3mi/hour. The return trip takes only 2.5 hours. What is the relative speed of the boat?

I know the total time of the trip is 7.5 hours and the current is +/- 3 of relative speed.

So.. I started with this equation...

7.5 = (Distance/(r+3)) + (Distance/(r-3))

In every example our textbook did of these types of problems, a distance was always given. I know you can manipulate the equation to d = rt, but I can't get d if I don't know r.

The instructor is saying this is solvable. I don't know mind scratching my head to figure it out as long as someone here can confirm it is indeed solvable. I don't think it is without a distance being given.