HIV POSITIVE

This topic has expert replies
Legendary Member
Posts: 1578
Joined: Sun Dec 28, 2008 1:49 am
Thanked: 82 times
Followed by:9 members
GMAT Score:720

HIV POSITIVE

by maihuna » Sat Aug 15, 2009 12:16 am
Suppose that the reliability of a HIV test is specified as follows:
Of people having HIV, 90% of the test detect the disease but 10% go undetected. Of people free of HIV, 99% of the test are judged HIV–ive but 1% are diagnosed as showing HIV+ive. From a large population of which only 0.1% have HIV, one person is selected at random, given the HIV test, and the pathologist reports him/her as HIV+ive. What is the probability that the person actually has HIV?
Charged up again to beat the beast :)

Master | Next Rank: 500 Posts
Posts: 113
Joined: Thu Jul 16, 2009 11:23 am
Thanked: 15 times
GMAT Score:730

by prindaroy » Sat Aug 15, 2009 8:57 pm
[(0.001)(0.9)]/[(0.999)(0.01)+(0.001)(0.9)] = 0.0826 or 8.26%. This will never be a GMAT question. Simply cannot do it without a calculator. The method behind this;

Truly HIV+/Total HIV +