A man can row three- quarters of a kilometer against the stream in 11.25 minutes and down the stream in 7.5 minutes. The speed ( in km/hr) of the man in still water is-

4 km/hr

5 km/hr

6 km/hr

6.5 km/hr

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উত্তর: 5 km/hr

Let the speed of the man and flow of the stream U and V respectively. Distance = 3/4 km Time taken to go upstream = 11.25 min = 11.25/60 hr Conbined speed upstream = (3/4) / (11.25/60) = 4 km/hr or, U - V = 4 or, V = U - 4 Time taken to go downstream = 7.5 min = 7.5/60 hr Conbined speed downstream = (3/4) / (7.5/60) = 6 km/hr or, U + V = 6 or, U + U - 4 = 6 or, 2U = 6 + 4 or, U = 10/2 = 5 km/hr

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