<PRE><B>Question 982837</B>
A boat travels 2km upstream and 2km back. the time for the round trip is 10 hours. the speed of the stream is 5km/hr whats the speed of the boat in still water?
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Avg speed of the round trip = 4/10 = 0.4 km/hr
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B = boat&#39;s speed
U = speed upstream = B-5 km/hr
D = speed downstream = B+5 km/r
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Avg speed = 2*U*D/(U+D)
2(B-5)*(B+5)/2B = 0.4
B^2 - 25 = 0.4B
5B^2 - 2B - 125 = 0
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{{{B = 0.2 + sqrt(2504)/10}}}
B =~ 5.204 km/hr
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