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Rajan

· started a discussion

· 1 Months ago

Not able to understand solution (Question: 48063.0 )

Not able to understand solution

Question:
A man can row \(9\cfrac{1}{3}\) kmph. in still water and finds that it takes time thrice as much time to row up than as to row down the same distance in the river. The speed of the current is?
Options:
A) \(3\cfrac{1}{3}\) kmph.
B) \(3\cfrac{1}{9}\) kmph.
C) \(4\cfrac{2}{3}\) kmph.
D) 14 kmph.
E) 15 kmph.
Solution:
Let the speed of current be x km/hr. 

Then, Speed in upstream = \((9{1\over3}-x)~km/hr\) = \(({28\over3}-x)~km/hr\)

Speed in downstream = \(({28\over3}+x)~km/hr\)

Since, distance is same. Hence, \(({28\over3}-x)\times3=({28\over3}+x)\)

\(\Rightarrow 28-3x={28+3x\over3}\)

\(\Rightarrow 12x = 56\)

\(\Rightarrow x = 4{2\over3}\)

Knowledge Expert

· commented

· 1 Months ago

first analyse quickly that what we need to calculate and what values we require to get it.
So here we need to get speed of current, for that we will need speed downstream and speed upstream, because we know
Speed of current = 1/2(a-b)
Let the speed upstream = x kmph
Then speed downstream is = 3x kmph
speed in still water = 1/2(a+b)=>1/2(3x+x)=>2x as per question we know, 2x=9 and 1/3=>2x=28/3=>x=14/3
So,
Speed upstream = 14/3 km/hr, Speed downstream 14 km/hr.
Speed of the current
=1/2[14−14/3]=14/3=4 and 2/3kmph
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