Time, Speed & Distance
Aptitude

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Q.

A motorboat whose speed is 15 km/hr in still water goes 30km downstream and comes back in four and a half hours. The speed of the stream is:

 A.

4.5 km/hr

 B.

6 km/hr

 C.

7 km/hr

 D.

5 km/hr

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Solution:
Option(D) is correct

Let the speed of the stream be '$s$' km/hr.

Then, upward speed = $(15−s)$ km/hr

and downward speed = $(15+s)$ km/hr

Therefore,

\(\dfrac{30}{(15+s)}+\dfrac{30}{(15-s)}=4.5\)

On solving this equation we get, $s$ = 5 km/hr

Edit: A typo in the solution has been corrected after it was pointed out by Vejayanantham TR.


(2) Comment(s)


Vejayanantham TR
 ()

it is not -4.5 , it is just 4.5


Deepak
 ()

Thank you, Vejayanantham for pointing it out. Corrected the typo.