SOLUTION: John can run his boat in the still water at a speed of 15 miles per hour. If he can go 12 miles downstream in the same time as it takes him to go 9 miles upstream, then what is the

Algebra ->  Customizable Word Problem Solvers  -> Misc -> SOLUTION: John can run his boat in the still water at a speed of 15 miles per hour. If he can go 12 miles downstream in the same time as it takes him to go 9 miles upstream, then what is the      Log On

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Question 209400: John can run his boat in the still water at a speed of 15 miles per hour. If he can go 12 miles downstream in the same time as it takes him to go 9 miles upstream, then what is the speed of the water currents?

Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
John can run his boat in the still water at a speed of 15 miles per hour. If he can go 12 miles downstream in the same time as it takes him to go 9 miles upstream, then what is the speed of the water currents?
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w = speed of the current
12/(15+w) = 9/(15-w) ( = time)
Cross multiply
12(15-w) = 9(15+w)
180-12w = 135+9w
21w = 45
w = 15/7 mph
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