A boat takes 9 h to travel a distance upstream and taken 3 h to travel the same distance downstream. If the speed of the boat in still water is 4 km/h, then what is the velocity of the stream?
Correct Answer: 2 km/h
Explanation:
Let velocity of the stream be x km/h
∴ Velocity of the boat downstream = (4 + x) km/h
and velocity of the boat upstream = (4 - x) km/h
According to the question, 3(4 + x) = 9(4 - x)
⇒ 12 + 3x = 36 - 9x
⇒ 12x = 24
∴ x = 2 km/h
