A boatman goes 4 km against the current of the stream in 4 hour and goes 1 km along the current in 20 minutes. How long will it take to go 6 km in stationary water?	Select:
A) 5 hours B) 1 hours C) 3 hours D) 2 hours E) 4 hours

Rationale: speed upstream = 4 / 4 = 1 km / hr speed downstream = 1 / ( 20 / 60 ) = 3 km / hr speed in still water = 1 / 2 ( 3 + 1 ) = 2 km / hr time taken to travel 6 km in still water = 6 / 2 = 3 hours answer : c
Answer: C