SOLUTION: speed of a boat in still water is 11km/hr. it can go 12 kms uptream and return downstream to the original pointin 2hours45minutes. find speed of stream.

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Question 934453: speed of a boat in still water is 11km/hr. it can go 12 kms uptream and return downstream to the original pointin 2hours45minutes. find speed of stream.
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
boat speed = 11 km/h
current speed = x km/h

against current = 11 - x
with current = 11 + x

Total distance = 12 km Total Time= 2.75 hours
Time upstream + time downstream = 2.75 hours

12 /( 11 - x )+ 12 /( 11 + x )= 2.75
12 ( 11 + x )+ 12 ( 11 - x )= 2.75 ( 121 - 1 X^2 )
132 + 12 x + 132 -12 x = 332.75 - 2.75 X^2
264 - -332.75 = -2.75 X^2
-68.75 = -2.75 X^2
-2.75 X^2= -68.75
x2= = 25
x= +/- 5
speed of current = 5 km/h