A man can row 18 km/h in still water. It takes him two times as long to row up as to row down the river. Find the rate of the stream.

Correct option is B

Given:
Speed of man= 18 km/h
downstream time = 2× upstream time
Solution:
Let speed of stream = s
Distance = d
Then,
Downstream time = $$\frac{d}{18+s}$$

Upstream time = $$\frac{d}{18-s}$$

As per the question,

​$$\frac{d}{18+s}=2\times\frac{d}{18-s}\\ \frac{18-s}{18+s}=\frac{2}{1}\\18-s = 36+2s\\3s = 18\\ s = 6 km/h\\$$

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