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  • A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:

A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:

Answers (1)

Speed =15km/hr

Distance d =30

let the speed of stream be x km/hr

Downstream time= 30/(15+x)

Upstream time =30/(15-x)

Given Total time =4 hours 30 mins =9/2 hr.

According the question

30{1/(15+x)+1/(15-x)}=9/2

10{(15+x+15-x)/(225-x2)}=3/2

300/(225-x2)=3/2

100/(225-x2)=1/2

200= 225-x2

x2=25

x=5 km/hr

Posted by

Ravindra Pindel

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