SOLUTION: A columbia river tugboat can go 12 mph in still water. It travels up the rivier 39 miles and back 30 miles in a total time of 6 hours. What is the speed of the current?

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Question 618517: A columbia river tugboat can go 12 mph in still water. It travels up the rivier 39 miles and back 30 miles in a total time of 6 hours. What is the speed of the current?
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
A columbia river tugboat can go 12 mph in still water. It travels up the river 39 miles and back 30 miles in a total time of 6 hours. What is the speed of the current?
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Upriver DATA:
distance = 39 miles ; rate = (12-c) mph; time = d/r = 39/(12-c) hrs.
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Downriver DATA:
distance = 30 miles ; rate + (12+c) mph ; time = d/r = 30/(12+c) hrs.
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Equation:
time + time = 6 hrs
39/(12-c) + 30/(12+c) = 6
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39(12+c) + 30(12-c) = 6(12-c)(12+c)
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829 + 9c = 864 - 6c^2
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6c^2 + 9c - 35 = 0
c = 1.7790 mph (speed of the current)
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Cheers,
Stan H.
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