Question 761700
Tonya's outboard can drive her boat at 7mph in still water. it takes her 10 minutes more to reach her friends camp 4 miles up the river than to return to her camp down river. What is the speed of the current?
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Upstream DATA:
distance = 4 miles ; rate = 7-c mph ; time = d/r = 4/(7-c) hrs
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Downstream DATA:
distance = 4 miles ; rate = 7+c mph ; time = d/r = 4/(7+c) hrs
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Equation:
down time - up time = 1/6 hr
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4/(7+c) - 4/(7-c) = 1/6
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24(7-c) - 24(7+c) = 7^2-c^2
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-48c = 49 - c^2
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c^2 - 48c - 49 = 0
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(c-49)(c+1) = 0

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Usable answer: c = 49
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Note: that answer doesn't make much sense if the boat's speed
in still water is only 7 mph.
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Cheers,
Stan H.
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