# Find the speed of the motor boat in still water , if stream running at 2 kmph ?

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A motor boat goes 10 km upstream and back again to starting point in 55 min.
Find the speed of the motor boat in still water , if stream running at 2 kmph ?

posted Jan 13, 2016

+1 vote

Let the speed of boat in still water=x km/hr
speed of stream (current)=2 km/hr
Then,
speed of boat in up stream=(x-2)km/hr=s1
speed of boat in downstream=(x+2)km/hr=s2
distance travel upstream=d1=10km
distance travel downstream=d2=10km
t1=d1/s1=10/((x-2)
t2=d2/s2=10/(x+2)
Total time taken=t=55min=55/60hr=11/12hr
t1+t2=t
[10/(x-2)]+[10/(x+2)]=11/12
x=22 0r x=-(2/11)
negative speed is not possible
so x=22km/hr
Ans :Speed of boat in still water is 22km/hr

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