A boatman goes 3 km against the current of the stream in 3 hour and goes 1 km along the current in 30 minutes. How long will it take to go 3 km in stationary water? Choose the correct choice from the following choices:
A) 5 hours	B) 4 hours	C) 3 hours	D) 2 hours	E) 1 hours

Rationale: "explanation : speed upstream = 3 / 3 = 1 km / hr speed downstream = 1 / ( 30 / 60 ) = 2 km / hr speed in still water = 1 / 2 ( 2 + 1 ) = 3 / 2 km / hr time taken to travel 3 km in still water = 3 / ( 3 / 2 ) = 6 / 3 = 2 hours answer : option d"
Answer: D