A man can row 15 km/hr in still water. It takes him twice as long row up as to row down the river. Find the rate of stream.

3 km/hr

3.5 km/hr

4 km/hr

5 km/hr

Let man's rate upstream be x km/hr. then, his rate downstream - 2x km/hr .'. Rate in still water = 1/2(2x + x) = 3x/2 km/hr. so, 3x/2 = 15 => 3x = 30 => x = 10 km/hr Rate upstream = 10 km/hr Rate downstream = 2*10 = 20 km/hr. hence, rate of stream = 1/2(20 -10) = 10/2 = 5 km/hr.

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