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Two men can swim in still water at the rate of 5 kmph. One swims upstream a distance equal to the width of the river (half a km) and back again; the other swims to a point straight across the river and back again. Assuming that the velocity of the river is 3 kmph, find the difference in times taken by two men. (Given answer is 3.75 min.)
I am getting a time difference of 1.8 min.
Please help
Sorry but your answer is wrong!!!!!!!
3.75 minutes is the correct answer.
for the first person, speed in first path=2 kmph (as he is swimming backward)
and in second path speed=8 kmph (as he is swimming forward)
so total time taken by him= (1/2) /2 + (1/2)/8 = 5/16 hours
now for second person he should swim in a direction so that when seen from ground his speed should be perpendicular to the flow of river so he should swim at an angle x, where sin x=3/5. so his speed will be 4 kmph in direction perpendicular to the flow of river.
So time taken by second person= (1/2)/4 + (1/2)/4 (as condition is same in both cases of second person)
so total time taken by second=1/4 hours.
so difference in time= (5/16 - 1/4) =1/16 hours = 3.75 minutes.
Hope you understand!!!!!!!!!!!!
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