document.write( "Question 347407: A boat travels 12 miles up the Mississippi River and 12 miles back down river in a total of eight hours. The rate of the boat in still water is four miles per hour. Find the speed of the current. \n" ); document.write( "

Algebra.Com's Answer #248415 by josmiceli(19441) $\"\"$ $\"About$

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given:
\n" ); document.write( " $\"r%5Bs%5D+=+4\"$ mi/hr
\n" ); document.write( " $\"d+=+12\"$ mi
\n" ); document.write( " $\"t%5B1%5D+%2B+t%5B2%5D+=+8\"$ hrs
\n" ); document.write( "Going upstream:
\n" ); document.write( " $\"12+=+%284+-+c%29%2At%5B1%5D\"$
\n" ); document.write( " $\"t%5B1%5D+=+12%2F%284-c%29\"$
\n" ); document.write( "Going downstream:
\n" ); document.write( " $\"12+=+%284+%2B+c%29%2A%288+-+t%5B1%5D%29\"$
\n" ); document.write( " $\"12+=+32+%2B+8c+-+4t%5B1%5D+-+c%2At%5B1%5D\"$
\n" ); document.write( "By substitution:
\n" ); document.write( " $\"12+=+32+%2B+8c+-+%284+%2B+c%29%2A%2812%2F%284+-+c%29%29\"$
\n" ); document.write( " $\"-20%2A%284+-+c%29+=+8c%2A%284+-+c%29+-+12%2A%284+%2B+c%29\"$
\n" ); document.write( " $\"20c+-+80+=+32c+-+8c%5E2+-+48+-+12c\"$
\n" ); document.write( " $\"8c%5E2++=+32\"$
\n" ); document.write( " $\"c%5E2+=+4+\"$
\n" ); document.write( " $\"c+=+2\"$
\n" ); document.write( "The speed of the current is 2 mi/hr
\n" ); document.write( "check answer:
\n" ); document.write( "Going upstream:
\n" ); document.write( " $\"12+=+%284+-+c%29%2At%5B1%5D\"$
\n" ); document.write( " $\"12+=+%284+-+2%29%2At%5B1%5D\"$
\n" ); document.write( " $\"2t%5B1%5D+=+12\"$
\n" ); document.write( " $\"t%5B1%5D+=+6\"$ hrs
\n" ); document.write( "Going downstream:
\n" ); document.write( " $\"12+=+%284+%2B+c%29%2A%288+-+t%5B1%5D%29\"$
\n" ); document.write( " $\"12+=+%284+%2B+2%29%2A%288+-+t%5B1%5D%29\"$
\n" ); document.write( " $\"8+-+t%5B1%5D+=+2\"$ hrs
\n" ); document.write( " $\"6+%2B+2+=+8\"$ hrs total
\n" ); document.write( "OK
\n" ); document.write( " \n" ); document.write( "

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