A tourist traveled on a motorboat against the current for 25 km. And then returned back on a raft. In the boat the tourist traveled for 10 hours less than on the raft. Find the speed of the current if the speed of the motorboat in still water is 12 km/hour.

Answer 1

I will assume that the speed of the raft is the speed of the current.
Let the speed of the current be x km/h

speed of boat against current = 12-x km/h
time with boat = 25/(12-x)
time on raft = 25/x

25/x - 25(12-x) = 10
divide by 5
5/x - 5/(12-x) = 2
multiply each term by x(12-x)
5(12-x) - 5x = 2x(12-x)
60 - 5x - 5x = 24x - 2x^2
2x^2 - 34x + 60 = 0
x^2 - 17x + 30 = 0
(x-2)(x-15) = 0
x = 2 or x = 15
but at a current of 15 km/h the boat would be going backwards, so

x = 2 , the speed of the current.