The velocity of a river is 2 km/hour. How much time is required to travel a boat in that river for

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20 Jul 2011 river

The velocity of a river is 2 km/hour. How much time is required to travel a boat in that river for 10 km. downstream then 10 km. upstream. Velocity of boat is 3km./hour in still water.

OPtion

1) 3 hrs
2) 4 hrs
3) 5 hrs
4) 6 hrs
5) 8 hrs
6) 12 hrs
7) 14 hrs
8) 15 hrs
9) 16 hrs
10) none of these

Solution

net velocity downstream = 3+2 = 5 km./hrs.
net velocity upstream = 3-2 = 1 km./hrs.
so total time required = (10/5) + (10/1)
= 2 + 10 = 12 hrs.

Correct Option: 6 Best Solution (0)