Question 115

A man can swim 3 km/hr. in still water. If the velocity of the stream is 2 km/hr., the time taken by him to swim to a place 10 km upstream and back is :

Solution

Given that speed of swimmer = 3km/hr

speed of river current = 2km/hr

Speed of swimmer in upstream = (3-2) km/hr = 1 km/hr

Speed of swimmer in downstream = (3+2) km/hr = 5 km/hr

Distance to be covered upstream = Distance to be covered downstream =10 km

So time taken in to and fro journey = $$\frac{10}{3-2} + \frac{10}{3+2}$$ = $$\frac{10}{1} + \frac{10}{5}$$ = 12 hour

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