The speed of a boat in still water is 10 km/hr. If it can travel 26 km downstream and 14 km upstream in the same time, the speed of the stream is:

A. 1 km/hr
B. 1.5 km/hr
C. 2 km/hr
D. 3 km/hr
Ans: D

Explanation:

Let the speed of the stream be x km/hr. Then,
Speed downstream = (10+x) km/hr, Speed upstream = (10 - x) km/hr.
=> 26/(10+x) = 14/(10-x) <=> 260 - 26x = 140 + 14x <=> 40x = 120
=> x = 3 km/hr.