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Old 07 February 2014, 08:00 PM
Steve Steve is offline
 
Join Date: 19 October 2002
Location: Charleston, SC
Posts: 4,773
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Another math problem that people often get wrong is this. A certain disease strikes 1 out of 1000 people, totally at random. There's a test for the disease that's 95% accurate. If you have the disease, there's a 95% chance the test will say positive, and a 5% chance it says negative, and if you don't have the disease there's a 95% chance the test says negative, and a 5% chance it says positive. You take the test, and it comes back positive. What are the chances you have the disease?

Answer: About 2%.
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