document.write( "Question 138377: a boat travels 100 miles downstream in the same length of time it travels upstream. if the boats speed in still water is 30 mph, find the speed of the current river. \n" ); document.write( "
Algebra.Com's Answer #101035 by stanbon(75887)\"\" \"About 
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the speed of the current must be zero.
\n" ); document.write( "Let the current speed be \"c\":
\n" ); document.write( "Upstream Data:
\n" ); document.write( "distance = 100 miles ; rate = 30-c mph ; Time = d/r = 100/(30-c) hrs
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\n" ); document.write( "Downstream DATA:
\n" ); document.write( "distance = 100 miles ; rate = 30+c mph ; Time = d/r = 100/30+c hrs
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\n" ); document.write( "EQUATION:
\n" ); document.write( "time up = time down
\n" ); document.write( "100/(30-c) = 100/(30+c)
\n" ); document.write( "30-c = 30+c
\n" ); document.write( "2c = 0
\n" ); document.write( "c = zero
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\n" ); document.write( "There is no upsteam or downstream on this particular river.
\n" ); document.write( "It must be a lake.
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\n" ); document.write( "Cheers,
\n" ); document.write( "Stan H.
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