Question

Speed of a boat in still water is 9 km/hr. It goes 12 km downstream and comes back to the starting point in three hours. What is the speed of water in the stream?

A 3 km/hr Correct Answer Incorrect Answer
B 4 km/hr Correct Answer Incorrect Answer
C 4.5 km/hr Correct Answer Incorrect Answer
D 5 km/hr Correct Answer Incorrect Answer
E None of these Correct Answer Incorrect Answer

Solution

Let the speed of the boat = 9km/hr Speed of current = x km/hr Speed upstream = (9 – x) km/hr Speed downstream = (9 + x) km/hr Time upstream + time downstream = 3 hours Time = distance/(speed ) 12/(9-x)+ 12/(9+x) = 3 x = 3 km/hr

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