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Wednesday 26 September 2018
Quantitative Aptitude : Boat and Streams
A man swims for 3 hours
downstream and then 3 hours upstream. In his whole process he covers a total
distance of 18 km. If the speed of the stream is 2 kmph, for what more time
will he have to swim upstream to reach the starting point?
Let his speed in still water be x kmph
ReplyDeletespeed of the stream = 2 kmph
speed downstream = (x+2) kmph
downstream distance covered = 3(x+2) km
speed upstream = (x-2) kmph
upstream distance covered = 3(x-2) km
Total distance covered = 18 km
3(x+2) + 3(x-2) = 18
6x = 18
x = 3
downstream distance covered = 3(x+2) = 3(3+2) = 15 km
upstream distance covered = 3(x-2) = 3(3-2) = 3 km
therefore he has to swim 15-3=12 km upstream to reach the starting point
speed upstream = (x-2) = 3-2 = 1 kmph
Required time = 12 / 1 = 12 hours