SOLUTION: Ian paddled a canoe 7 miles upstream in a river that has a current of 4 mph. He then turned around and paddled downstream until he reached his original starting place. If the entir

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Question 813203: Ian paddled a canoe 7 miles upstream in a river that has a current of 4 mph. He then turned around and paddled downstream until he reached his original starting place. If the entire trip took him 6 hours, how fast would Ian paddle in still water?
Found 2 solutions by stanbon, richwmiller:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
Ian paddled a canoe 7 miles upstream in a river that has a current of 4 mph. He then turned around and paddled downstream until he reached his original starting place. If the entire trip took him 6 hours, how fast would Ian paddle in still water?
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Upstream DATA:
distance = 7 miles ; rate = b-4 mph ; time = d/r = 7/(b-4) hrs
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Downstream DATA:
distance = 7 miles ; rate = b+4 mph ; time = d/r = 7/(b+4) hrs
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Equation:
time + time = 6 hrs
7/(b-4) + 7/(b+4) = 6
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7(b+4) + 7(b-4) = 6(b^2-16)
14b = 6b^2 - 96
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3b^2 - 7b -48 = 0
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Positive solution::
b = 5 1/3 mph (Ian's rate in still water)
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Cheers,
Stan H.
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Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
a+b=6,
(r+4)*a=7,
(r-4)*b=7
a = 3/4, b = 21/4, r = 16/3