Callie took 20 minutes to drive her boat upstream. Coming back later that day, at the same speed, it took her 15 minutes. If the current in the river is 5 km per hr, what was her boat speed?

Question

ranga · Answer

Assume boat speed is s
Upstream the boat speed relative to a stationary observer is (s - 5)
And the upstream travel time is 20 minutes.
So you can find the distance traveled.

Downstream the boat speed relative to a stationary observer is (s + 5)
And the downstream travel time is 15 minutes.
So you can find the distance traveled.

The distance traveled is the same in both directions.
Equate them and solve for s.