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kaushal

· started a discussion

· 1 Months ago

issue (Question: 111016.0 )

here time is constant then y ratios of time are taken??

Question:
A man rows boat to a place covering 72 km distance and back in 15 hours. He finds that he can row 3 km with the stream in the same time as 2 km against the stream. Find the speed of the stream.
Options:
A) 1 km/h
B) 2 km/h
C) 3 km/h
D) 4 km/h
Solution:
Ans: (b) Speed downstream : speed upsteam = 3 : 2 

\(\therefore\) Time taken to row downstream : Time taken to row upsteam = 2 : 3 

But, total time taken = 15 hours

\(\therefore\) Time taken to row downstream \(=\cfrac{2}{5}\times15\) hours = 6 hours

And time taken to row upstream = 15 - 6 = 9 hours.

\(\therefore\) Speed downstream \(=\cfrac{72}{6}=12\ km/h\)

And speed upstream \(=\cfrac{72}{9}=8\ km/h\)

\(\therefore\) Speed of the stream \(=\cfrac{12-8}{2}=2\ km/h\)

For Video Solution Click on the link given below:

Knowledge Expert

· commented

· 1 Months ago

Total time is constant but we have no information about individual time taken by downstream and upstream.
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