A man rows to a place 48 km distance and back in 14 hours. He finds that he can row 4 km with the stream in the same time as 3 km against the stream. The rate of the stream is:

A. 1 km/hr
B. 2.5 km/hr
C. 3 km/hr
D. 4 km/hr
Ans: A.

Explanation:

Suppose he moves 4 km downstream in x hours. Then,
Speed downstream = [4/x] km/hr, Speed upstream = [3/x] km/hr.
=> 48/(4+x) + 48/(3/x) = 14 or x = 1/2.
So, Speed downstream = 8 km/hr, Speed upstream = 6 km/hr.
Rate of the stream = 1/2 (8-6) km/hr = 1 km/hr