<PRE><B>Question 620028</B>
the speed of the boat in still water is 11km/hr.it can go 12km upstream and return downstream to the original point in 2hrs 45min. find the speed of the stream.
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let x=speed of stream
11+x=speed of boat downstream
11-x=speed of boat upstream
2 hr and 45 min=2.75 hr
Travel time=distance/speed
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12/(11+x)+12/(11-x)=2.75
LCD:(11+x)(11-x)
12(11-x)+12(11+x)=2.75(11+x)(11-x)=2.75(121-x^2)=332.75-2.75x^2
132-12x+132+12x=332.75-2.75x^2
264=332.75-2.75x^2
2.75x^2=332.75-264=68.75
x^2=68.75/2.75=25
x=5
speed of stream= 5 km/hr</PRE>