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Aptitude - Boats and Streams - Discussion

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"I never see what has been done; I only see what remains to be done."
- Marie Curie
13.

Speed of a boat in standing water is 9 kmph and the speed of the stream is 1.5 kmph. A man rows to a place at a distance of 105 km and comes back to the starting point. The total time taken by him is:

 [A]. 16 hours [B]. 18 hours [C]. 20 hours [D]. 24 hours

Explanation:

Speed upstream = 7.5 kmph.

Speed downstream = 10.5 kmph.

 Total time taken = 105 + 105 hours = 24 hours. 7.5 10.5

 Ramya said: (Mon, May 2, 2011 01:20:05 AM) How do you arrive at upstream and down stream speed.

 Bhavana said: (Sat, Jul 2, 2011 01:22:22 AM) How do you calculate upstream and downstream speed?

 Bhavana said: (Sat, Jul 2, 2011 01:38:34 AM) Speed upstream is 9+1.5 and downstream is 9-1.5. I think generally in stream sums we should calculate first the upstream and the downstream values.

 Kau said: (Sun, Sep 18, 2011 12:19:55 AM) You are wrong Bhavana, you have written opposite.

 Raju said: (Sat, Nov 5, 2011 08:08:08 PM) Time taken for up stream = 105/(9-1.5)=14h Time taken for down stream = 105/(9+1.5)=10h Total time taken= 14+10=24h

 Rakesh Kiit said: (Mon, Sep 3, 2012 12:46:15 AM) Average speed During the Journey = (2*(9+1.5)*(9-1.5))/(9+1.5)+ (9-1.5) so,Average speed=8.75 kmph so,Total time= total distance/average speed =(105*2)/8.75 = 24 hours.