Question 325255
Jane and Tariq took a canoeing trip, traveling 6 mi upsteam against a 2 mi/h current. 
They then returned to the same point downstream. 
If their entire trip took 4 h, how fast can they paddle in still water? (Hint: If r is their rate, in mi/h, in still water, their rate upstream is r-2 and their rate downstream is r+2)

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Upstream DATA:
rate = r-2 mph ; distance = 6 miles ; time = 6/(r-2) hrs.
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Downstream DATA:
rate = r+2 mph ; distance = 6 miles ; time = 6/(r+2) hrs
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Equations: 
time + time = 4 hrs
6/(r-2) + 6/(r+2) = 4 hrs
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6(r+2) + 6(r-2) = 4(r^2-4)
12r = 4r^2 - 16
r^2 - 3r - 4 = 0
(r-4)(r+1) = 0
Positive solution: 
r = 4 mph (rate in still water)
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Cheers,
Stan H.
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