<PRE><B>Question 263127</B>
The speed of a stream is 4 mph. A boat travels 7 miles upstream in the same time it takes to travel 15 miles downstream. What is the speed of the boat in still water?
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Upstream DATA:
distance = 7 miles ; rate = x-4 mph ; time = d/r = 7/(x-4) hrs.
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Downstream DATA:
distance = 15 miles ; rate = x+4 mph ; time = 15/(x+4) hrs
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Equation:
time = time
7/(x-4) = 15/(x+4)
7(x+4) = 15(x-4)
7x+28 = 15x-60
8x = 88
x = 11 mph (rate in still water)
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Cheers,
Stan H.</PRE>