A man can row a distance of 900 metres against the stream in 12 minutes and return to the starting point in 9 minutes. What is the speed (km/h) of the man in still water?
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 
Let the speed of man in still water be x
Let the speed of stream be y
Relative speed of man upstream
x - y = 0.9/(1/5)
(x - y) = 0.9 × 5
(x - y) = 4.5 →eq1
Realtive speed of man downstream
x + y = (0.9/9) × 60
(x + y) = 6 →eq2
Solving for x and y from eq1 and eq2
x = 4.5 + y
4.5 + 2y = 6
y = 1.5/2 = 0.725
x = 4.5 + 0.725
x = 5.25 km/hr