A man can row 12 kmph in still water. It takes him thrice as long to row up as to row down the river. Find the rate of the stream-

Question: A man can row 12 kmph in still water. It takes him thrice as long to row up as to row down the river. Find the rate of the stream-

Solution:
Given that,
Speed of man in still water = 12 km/h
Time upstream = 3 × Time downstream

Let,
Rate of the stream = x km/h

Now,
Downstream speed = 12 + x
Upstream speed = 12 - x

And, let the distance travelled is = D km

According to the Question,
Time taken upstream = 3 × (Time taken downstream)
D/(12 - x) = 3 × {D/(12 + x)}
⇒ 1/(12 - x) = 3/(12 + x)
⇒ 12 + x = 36 - 3x
⇒ 4x = 24
∴ x = 6

So, rate of the stream = 6 km/h