Enigma 1636: Risky business
12 December 2011
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From New Scientist #2802, 5th March 2011 [link]
Just before Christmas in Joe’s town, population 20,775, there was a bug going around, which, it was known later, had affected just 75 people. At the time the only test that could detect the bug was just 92 per cent accurate and was never used. Joe wondered, if all the population had been tested, what percentage of those who came up positive would actually have had the bug.
What would the percentage have been?