document.write( "Question 169265: Julie and Eric row their boat (at a constant speed) 45 miles downstream for 5 hours, helped by the current. Rowing at the same rate, the trip back against the current takes 9 hours. Find the rate of the current. \n" ); document.write( "
Algebra.Com's Answer #124813 by josmiceli(19441)\"\" \"About 
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Let the current be \"s\"
\n" ); document.write( "Let the rate of the boat with no current be \"r\"
\n" ); document.write( "With the current:
\n" ); document.write( "\"d+=+%28r+%2B+s%29%2At\"
\n" ); document.write( "Against the current:
\n" ); document.write( "\"d+=+%28r+-+s%29%2At\"
\n" ); document.write( "-------------------
\n" ); document.write( "Given:
\n" ); document.write( "\"45+=+%28r+%2B+s%29%2A5\"
\n" ); document.write( "\"45+=+%28r+-+s%29%2A9\"
\n" ); document.write( "Rewriting these,
\n" ); document.write( "\"5r+%2B+5s+=+45\"
\n" ); document.write( "\"9r+-+9s+=+45\"
\n" ); document.write( "Multiply the 1st by \"9\" and the 2nd by \"5\"
\n" ); document.write( "\"45r+%2B+45s+=+45%2A9\"
\n" ); document.write( "\"45r+-+45s+=+45%2A5\"
\n" ); document.write( "Add these equations
\n" ); document.write( "\"90r+=+45%2A14\"
\n" ); document.write( "Divide both sides by \"45\"
\n" ); document.write( "\"2r+=+14\"
\n" ); document.write( "\"r+=+7\"
\n" ); document.write( "Substitute this back into a given equation
\n" ); document.write( "\"45+=+%287+%2B+s%29%2A5\"
\n" ); document.write( "\"9+=+7+%2B+s\"
\n" ); document.write( "\"s+=+2\"
\n" ); document.write( "The rate of the current is 2 mi/hr
\n" ); document.write( "check:
\n" ); document.write( "\"45+=+%28r+%2B+s%29%2A5\"
\n" ); document.write( "\"45+=+%287+%2B+2%29%2A5\"
\n" ); document.write( "\"45+=+45\"
\n" ); document.write( "------------
\n" ); document.write( "\"45+=+%28r+-+s%29%2A9\"
\n" ); document.write( "\"45+=+%287+-+2%29%2A9\"
\n" ); document.write( "\"45+=+45\"
\n" ); document.write( "OK \n" ); document.write( "
\n" );