document.write( "Question 631013: After 5 hours of painting, Jess asked the assistance of Jon. Together they finished the job in 4 more hours. Had Jon joined in an hour after Jess started working, the job would have been finished in 7 hours. How long would it have taken Jess to paint the house alone \n" ); document.write( "
Algebra.Com's Answer #397344 by josmiceli(19441)\"\" \"About 
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Let \"+r%5B1%5D+\" = Jess's rate of painting in jobs/hr
\n" ); document.write( "Let \"+r%5B2%5D+\" = Jon's rate of painting in jobs/hr
\n" ); document.write( "--------------
\n" ); document.write( "In 5 hours Jess gets \"+5r%5B1%5D+\" fraction of the job done
\n" ); document.write( "In 1 hour jess get \"+1%2Ar%5B1%5D+\" fraction of the job done
\n" ); document.write( "--------------
\n" ); document.write( "given:
\n" ); document.write( "(1) \"+5r%5B1%5D+%2B+4%2A%28+r%5B1%5D+%2B+r%5B2%5D+%29+=+1+\" ( 1 means the whole job is done )
\n" ); document.write( "(2) \"+1%2Ar%5B1%5D+%2B+7%2A%28+r%5B1%5D+%2B+r%5B2%5D+%29+=+1+\"
\n" ); document.write( "---------------------------
\n" ); document.write( "(1) \"+9r%5B1%5D+%2B+4r%5B2%5D+=+1+\"
\n" ); document.write( "(2) \"+8r%5B1%5D+%2B+7r%5B2%5D+=+1+\"
\n" ); document.write( "-------------------
\n" ); document.write( "Multiply both sides of (1) by \"+7+\"
\n" ); document.write( "Multiply both sides of (2) by \"+4+\"
\n" ); document.write( "and subtract (2) from (1)
\n" ); document.write( "(1) \"+63r%5B1%5D+%2B+28r%5B2%5D+=+7+\"
\n" ); document.write( "(2) \"+-32r%5B1%5D+-+28r%5B2%5D+=+-4+\"
\n" ); document.write( "\"+31r%5B1%5D+=+3+\"
\n" ); document.write( "\"+r%5B1%5D+=+3%2F31+\"
\n" ); document.write( "This means Jess can paint 3 houses in 31 hrs
\n" ); document.write( "\"+3%2F31+=+1%2Fx+\"
\n" ); document.write( "\"+10.333+\"
\n" ); document.write( "He could paint the house alone in 10 hrs and 20 min
\n" ); document.write( "check:
\n" ); document.write( "(1) \"+9%2A%283%2F31%29+%2B+4r%5B2%5D+=+1+\"
\n" ); document.write( "(1) \"+4r%5B2%5D+=+31%2F31+-+27%2F31+\"
\n" ); document.write( "(1) \"+4r%5B2%5D+=+4%2F31+\"
\n" ); document.write( "(1) \"+r%5B2%5D+=+1%2F31+\"
\n" ); document.write( "and
\n" ); document.write( "(2) \"+8%2A%283%2F31%29+%2B+7%2A%281%2F31%29+=+1+\"
\n" ); document.write( "(2) \"+24%2F31+%2B+7%2F31+=+31%2F31+\"
\n" ); document.write( "(2) \"+24+%2B+7+=+31+\"
\n" ); document.write( "(2) \"+31+=+31+\"
\n" ); document.write( "OK
\n" ); document.write( "
\n" );