Infected? - math puzzle
| Suppose that 1 out of 1000 people of a specific country are infected with the deadly X-virus. An inhabitant of that country goes the hospital and gives some blood for a survey. Her blood is checked on the X-virus by a test which gives a correct outcome in 99% of the cases. The test points out that the woman is infected. After the investigation, a doctor tells the woman that he is 99% sure that she is infected with the X-virus. Can the doctor be right by making this worrying statement? |
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Answer
The doctor is not right, he has no ground on making the woman feel so uncomfortable. The probablility that the woman really is infected is only 9.0%.
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