A motorboat can travel at 5 km hr in still water It travelled 90 km downstream in a river and then r...........

Quant (SSC) Boats and Streams

A motorboat can travel at 5 km/hr in still water. It travelled 90 km downstream in a river and then returned, taking altogether 100 hours. Find the rate of flow of the river.

3 km/hr

3.5 km/hr

2 km/hr

4 km/hr

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Explanation:

Speed of boat in still water = x = 5 km/hr.
Let rate of flow of river = y km/hr.
∴ Speed of u/s = 5- y and speed of d / s = 5 + y
∴ 90/(5+y) + 90/(5-y) = 100
⇒ y = 4 km/hr.