document.write( "Question 777735: A can do a work in 12 days ;B in 6 days and C in 3 days.A and B start working together and after a day,C joins them.The total number of days required to complete the work is
\n" ); document.write( "(A) 16/7 days (B) 9/7 days (C) 15/7 days (D) 8/7 days \n" ); document.write( "

Algebra.Com's Answer #474242 by Edwin McCravy(20056) $\"\"$ $\"About$

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document.write( "Jobs done = (rate)×(time), or rather \r\n" );
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document.write( "Let's get the work rates in fraction of a job per day:\r\n" );
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document.write( "A's rate is  of a job per day.\r\n" );
document.write( "B's rate is  of a job per day.\r\n" );
document.write( "C's rate is  of a job per day.\r\n" );
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document.write( "A&B's combined rate is \r\n" );
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document.write( "+ = + =  =  of a job per day.\r\n" );
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document.write( "A&B&C's combined rate is \r\n" );
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document.write( "++ = ++ =  of a job per day.\r\n" );
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document.write( "When A&B worked for 1 day they did: \r\n" );
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document.write( "rate×time = ·1 =  of the job.\r\n" );
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document.write( "That left  of the job still undone.\r\n" );
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document.write( "Then C joined them for X days.\r\n" );
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document.write( "So when A&B&C worked for X days they did:\r\n" );
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document.write( "rate×time = X \r\n" );
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document.write( "and that must equal the remaining  of the job\r\n" );
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document.write( "So the equation is X = \r\n" );
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document.write( "Multiply both sides by 12\r\n" );
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document.write( "                   28X = 36\r\n" );
document.write( "                     X = 36/28\r\n" );
document.write( "                     X = 9/7 days.\r\n" );
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document.write( "Edwin

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