in still water. It travelled 91 km downstream in a river and then returned, taking altogether 20 hours. Find the rate of flow of river.
A) 3 km/hrs
B) 6 km/hrs
C) 5 km/hrs
D) 4 km/hrs
Correct Answer: A
Solution :
Speed of boat
Let rate of flow of river 
Relative speed during upstream 
Relative speed during downstream 
Time taken by boat to travel 91 kms upstream and downstream = 20 hours So, 
So, rate of flow of river 
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