document.write( "Question 1165824: Mark, Lex, and Bren can finish a job 12,16, and 19 hours, respectively. Mark and Lex worked together for 4 hours. Lex got tired so Bren worked in place of him until the job is finished. How long did Mark work? \n" ); document.write( "
Algebra.Com's Answer #790333 by Edwin McCravy(20060) $\"\"$ $\"About$
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document.write( "Make the following chart.  Fill in the times, letting the time that\r\n" );
document.write( "only Mark and Bren worked together after Lex quit be t.  When they\r\n" );
document.write( "did the whole job themselves we put 1 for the part of a job done, which\r\n" );
document.write( "means 100% of the job was done.\r\n" );
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document.write( "     | Part of  |  Rate   |   Time  |\r\n" );
document.write( "     |  job     |   in    |   taken |\r\n" );
document.write( "     |  done    | jobs/hr |  in hrs |\r\n" );
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document.write( "Mark |   1 (all)|         |   12    |\r\n" );
document.write( "Lex  |   1      |         |   16    |\r\n" );
document.write( "Bren |   1      |         |   19    |\r\n" );
document.write( "------------------------------------\r\n" );
document.write( "Mark |          |         |    4    |            \r\n" );
document.write( "Lex  |          |         |    4    |\r\n" );
document.write( "Mark |          |         |    t    |    \r\n" );
document.write( "Bren |          |         |    t    |\r\n" );
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document.write( "First we use the top three to get expressions for their rates\r\n" );
document.write( "by dividing the part of job done (1) by the time.\r\n" );
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document.write( "     | Part of  |  Rate   |   Time  |\r\n" );
document.write( "     |  job     |   in    |   taken |\r\n" );
document.write( "     |  done    | jobs/hr |  in hrs |\r\n" );
document.write( "------------------------------------\r\n" );
document.write( "Mark |   1 (all)|  1/12   |   12    |\r\n" );
document.write( "Lex  |   1      |  1/16   |   16    |\r\n" );
document.write( "Bren |   1      |  1/19   |   19    |\r\n" );
document.write( "------------------------------------\r\n" );
document.write( "Mark |          |  1/12   |    4    |            \r\n" );
document.write( "Lex  |          |  1/16   |    4    |\r\n" );
document.write( "Mark |          |  1/12   |    t    |    \r\n" );
document.write( "Bren |          |  1/19   |    t    |\r\n" );
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document.write( "Next we multiply the the rates by the time to get the\r\n" );
document.write( "parts of a job done.\r\n" );
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document.write( "     | Part of  |  Rate   |   Time  |\r\n" );
document.write( "     |  job     |   in    |   taken |\r\n" );
document.write( "     |  done    | jobs/hr |  in hrs |\r\n" );
document.write( "------------------------------------\r\n" );
document.write( "Mark |   1 (all)|  1/12   |   12    |\r\n" );
document.write( "Lex  |   1      |  1/16   |   16    |\r\n" );
document.write( "Bren |   1      |  1/19   |   19    |\r\n" );
document.write( "------------------------------------\r\n" );
document.write( "Mark |  4/12    |  1/12   |    4    |            \r\n" );
document.write( "Lex  |  4/16    |  1/16   |    4    |\r\n" );
document.write( "Mark |  t/12    |  1/12   |    t    |    \r\n" );
document.write( "Bren |  t/19    |  1/19   |    t    |\r\n" );
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document.write( "Those four parts of a job below the second dotted line must\r\n" );
document.write( "add to be 1 job.\r\n" );
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document.write( "Reduce the fractions that will reduce:\r\n" );
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document.write( "Multiply through by LCD of 228 \r\n" );
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document.write( "That's the number of hours he worked with Bren.\r\n" );
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document.write( "The total time Mark worked was the 4 hours he worked with Lex only\r\n" );
document.write( "plus the 3.064516129 hours he worked with Bren only after Lex quit\r\n" );
document.write( "or \r\n" );
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document.write( "7.064516129 hours.    <--answer\r\n" );
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document.write( "Edwin
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