Mugdho wrote:
A motor boat takes 12 hours to go downstream and it takes 24 hours to return the same distance. what is the time taken by boat in still water?
a)12
b)14
c)16
d)18
e)20
Posted from my mobile device
Let the distance be d, and the speed of motorboat and water be m and w.
UpstreamWater is against the boat, so speed = m-w
Time taken = \(24=\frac{d}{m-w}…….d=24m-24w\)
DownstreamWater is moving in same direction as the boat, so speed = m+w
Time taken = \(12=\frac{d}{m-w}…….d=12m-12w\)
Equating the distances in two cases => 12m+12w=24m-24w………..12m=36w……….m=3w
Substituting in any of the equations we get
\(12=\frac{d}{\frac{m}{3}+m}= \frac{d}{\frac{4m}{3}+m}…………..12*\frac{4}{3}=\frac{d}{m}=16\) hrs
C
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