document.write( "Question 1185500: The probability of a randomly selected adult in one country being infected with a certain virus is 0.004 . In tests for the virus, blood samples from 24 people are combined. What is the probability that the combined sample tests positive for the virus? Is it unlikely for such a combined sample to test positive? Note that the combined sample tests positive if at least one person has the virus. \n" ); document.write( "

Algebra.Com's Answer #816332 by ikleyn(52781) $\"\"$ $\"About$

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\n" ); document.write( "The probability of a randomly selected adult in one country being infected with a certain virus is 0.004.
\n" ); document.write( "In tests for the virus, blood samples from 24 people are combined. What is the probability that the combined sample tests
\n" ); document.write( "positive for the virus? Is it unlikely for such a combined sample to test positive?
\n" ); document.write( "Note that the combined sample tests positive if at least one person has the virus.
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document.write( "Let me re-formulate the problem in clear short EQUIVALENT form.\r\n" );
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document.write( "       If the probability of the event is 0.004, what is the probability \r\n" );
document.write( "       that in 24 independent trials it will happen at least once ?\r\n" );
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document.write( "The probability that it will not happen, is  0.996.\r\n" );
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document.write( "The probability that it will not happen in 24 trials is   = 0.908289.\r\n" );
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document.write( "The probability that it will happen at least once in 24 trial is the complement to it\r\n" );
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document.write( "    P = 1 -  = 1 - 0.908289 = 0.091711.    ANSWER\r\n" );
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