document.write( "Question 270049: It takes a couple four hours to row 28 miles with the river current. If it takes them 7 hours to cover the same distance when rowing against the current, find the speed of the river current \n" ); document.write( "

Algebra.Com's Answer #197886 by josmiceli(19441) $\"\"$ $\"About$

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$\"b\"$ = speed of boat in still water
\n" ); document.write( " $\"c\"$ = speed of current
\n" ); document.write( "With the current:
\n" ); document.write( " $\"d+=+%28b+%2B+c%29%2At%5B1%5D\"$
\n" ); document.write( "Against the current:
\n" ); document.write( " $\"d+=+%28b+-+c%29%2At%5B2%5D\"$
\n" ); document.write( "----------------------
\n" ); document.write( "given:
\n" ); document.write( " $\"d+=+28\"$ mi
\n" ); document.write( " $\"t%5B1%5D+=+4\"$ hrs
\n" ); document.write( " $\"t%5B2%5D+=+7\"$ hrs
\n" ); document.write( "-----------------------
\n" ); document.write( " $\"d+=+%28b+%2B+c%29%2At%5B1%5D\"$
\n" ); document.write( " $\"28+=+%28b+%2B+c%29%2A4\"$
\n" ); document.write( "(1) $\"4b+%2B+4c+=+28\"$
\n" ); document.write( "and
\n" ); document.write( " $\"d+=+%28b+-+c%29%2At%5B2%5D\"$
\n" ); document.write( " $\"28+=+%28b+-+c%29%2A7\"$
\n" ); document.write( "(2) $\"7b+-+7c+=+28\"$
\n" ); document.write( "----------------------
\n" ); document.write( "(1) $\"4b+%2B+4c+=+28\"$
\n" ); document.write( "(1) $\"b+%2B+c+=+7\"$
\n" ); document.write( "and
\n" ); document.write( "(2) $\"7b+-+7c+=+28\"$
\n" ); document.write( "(2) $\"b+-+c+=+4\"$
\n" ); document.write( "and
\n" ); document.write( "(2) $\"b+%2B+c+=+7\"$
\n" ); document.write( "(1) $\"b+-+c+=+4\"$
\n" ); document.write( " $\"2b+=+11\"$
\n" ); document.write( " $\"b+=+5.5\"$
\n" ); document.write( "And, from (2),
\n" ); document.write( " $\"b+-+c+=+4\"$
\n" ); document.write( " $\"5.5+-+c+=+4\"$
\n" ); document.write( " $\"c+=+5.5+-+4\"$
\n" ); document.write( " $\"c+=+1.5\"$
\n" ); document.write( "The speed of the river current is 1.5 mi/hr
\n" ); document.write( "check:
\n" ); document.write( " $\"28+=+%28b+%2B+c%29%2A4\"$
\n" ); document.write( " $\"28+=+%285.5+%2B+1.5%29%2A4\"$
\n" ); document.write( " $\"28+=+7%2A4\"$
\n" ); document.write( " $\"28+=+28\"$
\n" ); document.write( "and
\n" ); document.write( " $\"28+=+%28b+-+c%29%2A7\"$
\n" ); document.write( " $\"28+=+%285.5+-+1.5%29%2A7\"$
\n" ); document.write( " $\"28+=+4%2A7\"$
\n" ); document.write( " $\"28+=+28\"$
\n" ); document.write( "OK
\n" ); document.write( " \n" ); document.write( "

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