(A) 2.4 Km/h
(B) 5.6 Km/h
(C) 7.5 Km/h
(D) 8.9 Km/h
Correct Option is: C
Given that, time taken to travel upstream = 3 × time taken to travel downstream
When distance is constant, speed is inversely proportional to the time
Hence, 3 × speed upstream = speed downstream
Let speed upstream =x
Then speed downstream =3x
we have, 1/2(x+3x) = speed in still water
i.e., 2x =15 → x=7.5
i.e., speed upstream =7. 5 km/hr
Rate of stream =1/2(3x−x)= x = 7.5 km/hr