<PRE><B>Question 981685</B>
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c=speed of current
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time upstream=distance/rate=2.5mi/(20mph-c)
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time downstream=distance/rate=2.9mi/(20mph+c)
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Since it takes the same amount of time:
2.5mi/(20mph-c)=2.9mi/(20mph+c) Cross multiply.
(2.5mi)(20mph+c)=(2.9mi)(20mph-c)
50 mi^2/hr+2.5c mi=58mi^2/hr-2.9c mi Subtract 50mi^2/hr from each side.
2.5c mi=8mi^2/hr-2.9c mi Add 2.9c mi to each side.
5.4c mi=8mi^2/hr Divide each side by 5.4 mi.
c=1.48 mi/hr ANSWER: The rate of the current was 1.48 mph.
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CHECK:
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2.5mi/(20mph-c)=2.9mi/(20mph+c)
2.5mi/(20mph-1.48mph)=2.9mi/(20mph+1.48mph)
2.5mi/18.52mph=2.9mi/21.48mph
0.135 hr=0.135 hr
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