A man rows a boat downstream in 3 hour & returns back the same distance upstream in 6 hours. If the speed of stream is 2 km/hr, then the speed of the boat in still water is:
Answer & explanation
Correct answer: option 1
Let the speed of the boat be x km/h.
& speed of the stream = 2 km/h
Down stream speed = x + 2 km/h
Up stream speed = x – 2 km/h
Down stream time = 3 hours
Up stream time = 6 hours
Distance for both is same.
$∵ \frac{D}{x+2}=3$ ⇒ D = 3x + 6
& $\frac{D}{x-2}=6$ ⇒ D = 6x - 12
∴ 6x - 12 = 3x + 6 ⇒ 3x = 18
x = 6 km/h