Concept
What is the probability that someone coming out of a voting booth has a Twitter account?
Stephen Davies, Ph.D. Version 2.2.2 Through Discrete Mathematics A Cool Brisk Walk / Chapter 1
"75% of Twitter users vote, whereas only about half of people in general vote. Now say that about one out of every three people are on Twitter. If you see someone emerge from a voting booth, what’s the probability they have a Twitter account? The relevant probabilities here are Pr(vote | Twitter) = .75, Pr(vote) = .5, and Pr(Twitter) = 1/3. By Bayes’ Theorem, Pr(Twitter | vote) = Pr(vote | Twitter) · Pr(Twitter) / Pr(vote) = .75 · .333 / .5 = .5. So although only a third of people tweet, the chances are 50-50 that someone tweets once you see them coming out of a voting booth."
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