Time, Speed & Distance

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A boatman rows to a place 45 km distant and back in 20 hour. He finds that he can row 12 km with the stream in the same time as 4 km against the stream. Find the speed of the stream.


3 km/hr


2.5 km/hr


4 km/hr


3.5 km/hr

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Option(A) is correct

Ratio of time taken for up and down = $3:1$

Out of 20 hr he took 15 hr for up and 5 for down.

Speed up = \(\dfrac{45}{15}=3\)

and down = \(\dfrac{45}{5}=9\)

Hence speed of stream 

\((9−3)\times \dfrac{1}{2}\)

3 km/hr


(2) Comment(s)


How is the ratio found out?


Was it supposed to be (9-3) x 1/2?