document.write( "Question 149493: In a shop there are 20 customers, 18 of whom will make a purchase. If three customers are selected, one at a time, at random, what is the probability that all will make a purchase? Is it 0.7717, 0.7605, 0.8524, or 0.8808.\r
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Algebra.Com's Answer #109676 by Edwin McCravy(20059) $\"\"$ $\"About$

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In a shop there are 20 customers, 18 of whom will make a purchase. If three customers are selected, one at a time, at random, what is the probability that all will make a purchase? Is it 0.7717, 0.7605, 0.8524, or 0.8808.
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document.write( "It's not any of those.  It's 0.7158\r\n" );
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document.write( "P(1st chosen will purchase \r\n" );
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document.write( "      AND \r\n" );
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document.write( "           2nd chosen will purchase \r\n" );
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document.write( "                  AND\r\n" );
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document.write( "                      3rd chosen will purchase)\r\n" );
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document.write( "                            =\r\n" );
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document.write( "P(1st chosen will purchase) \r\n" );
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document.write( "TIMES\r\n" );
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document.write( "P(2nd chosen will purchase, given that the 1st chosen will purchase)\r\n" );
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document.write( "TIMES\r\n" );
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document.write( "P(3rd chosen will purchase, given that the 1st and 2nd chosen will purchase)\r\n" );
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document.write( " or rounded to ten-thousandths,\r\n" );
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document.write( "You can also do it using combinations: \r\n" );
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document.write( "Stanbon's solution is incorrect because \r\n" );
document.write( "the choices are not independent. Binomial\r\n" );
document.write( "probabilities are ONLY for independent choices.\r\n" );
document.write( "The choices are not independent because the \r\n" );
document.write( "probability of selecting the second one as a \r\n" );
document.write( "purchaser CHANGES after selecting the first one. \r\n" );
document.write( "Also the probability of selecting the third one \r\n" );
document.write( "as a purchaser CHANGES after selecting the \r\n" );
document.write( "first two.\r\n" );
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document.write( "Edwin

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