SOLUTION: Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minutes longer to get there than to return. How fast will her bo

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Question 175008: Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water?
Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website!
Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water?
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Upstream DATA:
distance = 5 miles; rate = b-4 mph ; time = d/r = 5/(b-4) hrs
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Downstream DATA:
distance = 5 miles; rate = b+4 mph ; time = 5/(b+4) hrs.
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Equation:
uptime - downtime = 1/3 hr
5/(b-4) - 5/(b+4) = 1/3
5(b+4) - 5(b-4) = (1/3)(b^2-16)
40 = (1/3)(b^2-16)
b^2 - 16 = 120
b^2 = 136
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Positive solution:
b = 11.66 mph (boat speed in quiet water)
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Cheers,
Stan H.