Time, Speed & Distance

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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:


4.5 km/hr


6 km/hr


7 km/hr


5 km/hr

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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



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


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