Easy Time, Speed & Distance Solved QuestionAptitude Discussion

 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

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.