document.write( "Question 1192319: 50% people use cell phone for writing notes,40% use paper,20% people use both,if a person is selected at random find the probability that he uses neither for taking notes?
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Algebra.Com's Answer #824221 by Edwin McCravy(20081)\"\" \"About 
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document.write( "It can be done by formula or Venn diagram.  The Venn diagram method\r\n" );
document.write( "is better for understanders.  Formulas are better for memorizers.\r\n" );
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document.write( "Realize that the probability that a person selected at random fits \r\n" );
document.write( "a certain description is EQUAL TO the percentage of people who fit \r\n" );
document.write( "that certain description\r\n" );
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document.write( "Since both \"PHONE\" and \"PAPER\" begin with the letter \"P\", I'll use \r\n" );
document.write( "\"PH\" for the set of people who use phones (the red circle) and \"PA\" \r\n" );
document.write( "for the set of people who use paper (the blue circle).\r\n" );
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document.write( "The big rectangle contains all the people.\r\n" );
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document.write( "Since 20% use both, we put \"20%\" in the region that in BOTH circles:\r\n" );
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document.write( "Since 50% use a phone, the entire red circle must contain 50% and since\r\n" );
document.write( "20% of the red circle is in the part that is common to both circles,\r\n" );
document.write( "the remaining 50%-20%=30% is already in the left part of the red circle, \r\n" );
document.write( "we must put the other 30% in the left part of the red circle.\r\n" );
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document.write( "[Be sure to understand why it couldn't work to put the entire 50% in the left\r\n" );
document.write( "part of the red circle, as many students tend to want to do, because they want\r\n" );
document.write( "to put the whole 50% someplace instead of breaking it down into 20% and 30%.]\r\n" );
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document.write( "Since 40% use paper, the entire blue circle must contain 40% and since\r\n" );
document.write( "20% of the blue circle is in the part that is common to both circles,\r\n" );
document.write( "the remaining 40%-20%=20% is in the right part of the blue circle, so we\r\n" );
document.write( "put the other 20% in the right part of the blue circle.\r\n" );
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document.write( "But we have not yet accounted for the percentage of people who use\r\n" );
document.write( "neither phone nor paper. And, that's what we want.\r\n" );
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document.write( "So we add what we've accounted for 30%+20%+20%=70% and subtract it \r\n" );
document.write( "from 100%. 100%-70%=30%   Then we put 30% outside both circles but \r\n" );
document.write( "inside the rectangle for those who do not use either their phones \r\n" );
document.write( "or paper to write notes.\r\n" );
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document.write( "So we see that the answer is 30%.\r\n" );
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document.write( "Edwin
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