A man can row a boat at speed 8 km/h in still water. It takes thrice as long to row upstream as it does to row downstream. Find the speed of the stream (in km/h).
Show answer & explanation
Correct answer: B
Explanation
The correct answer is Option 2 i.e. 4.
Speed of the boat = 8 km/hr
Speed of the stream = y km/hr
So,
Upstream speed = 8 - y
Downstream speed = 8 + y
It takes thrice as long to row upstream as it does to row downstream
Let the distance be D
⇒ D/(8 - y) = 3 × D/(8 + y)
⇒ 1/(8 - y) = 3/(8 + y)
⇒ (8 + y) = 3(8 - y)
⇒ 8 + y = 24 - 3y
⇒ 4y = 16
⇒ y = 4
Thus, the speed of the stream is 4 km/hr