SOLUTION: Please help. The Columbia River flows at a rate of 2mph for the length of a popular boating route. In order for a motorized dinghy to travel 3 mi upriver and then return in a total
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Question 687746: Please help. The Columbia River flows at a rate of 2mph for the length of a popular boating route. In order for a motorized dinghy to travel 3 mi upriver and then return in a total of 4 hrs, how fast must the boat be able to travel in still water?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
The Columbia River flows at a rate of 2mph for the length of a popular boating route. In order for a motorized dinghy to travel 3 mi upriver and then return in a total of 4 hrs, how fast must the boat be able to travel in still water?
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Upriver DATA:
distance = 3 miles ; rate = b-2 mph ; time = d/r = 3(b-2) hrs
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Downriver DATA:
distance = 3 miles ; rate + b+2 mph ; time = d/r = 3/(b+2) hrs
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Equation:
time + time = 4 hrs
3/(b-2) + 3/(b+2) = 4
3(b+2) + 3(b-2) = 4(b^2-4)
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6b = 4b^2 -16
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2b^2 - 3b - 8 = 0
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b = [3 +- sqrt(9-4*2*-8)]/4
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Positive solution:
b = [3 + sqrt(73)]/4
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b = 2.89 mph (speed of the boat in still water)
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Cheers,
Stan H.
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