Time, Speed & Distance
Aptitude

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Q.

A man can row 50 km upstream and 72 km downstream in 9 hours. He can also row 70 km upstream and 90 km downstream in 12 hours. Find the rate of current.

 A.

3 km/hr

 B.

8 km/hr

 C.

4 km/hr

 D.

None of these

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Solution:
Option(D) is correct

Let $x$ and $y$ be the upstream and downstream speed respectively.

Hence

\(\dfrac{50}{x}+\dfrac{72}{y}=9\) and

\(\dfrac{70}{x}+\dfrac{90}{y}=12\)

Solving for $x$ and $y$ we get $x=10$ km/hr and $y=18$ km/hr

We know that: 

\(\text{Speed of the stream}\)

\(=\dfrac{1}{2}\times \text{(downstream speed - upstream speed)}\)

\(=\dfrac{1}{2}(18-10)\)

4 km/hr


(1) Comment(s)


Jeetu
 ()

You are saying 4kmph is the answer but then why the answer is marked as 'None of these'