QUESTION
(8) A spam filter is designed by looking at commonly occurring phrases in spam. Suppose that $80 \%$ of email is spam. In $10 \%$ of the spam emails, the phrase "free money" is used, whereas this phrase is only used in $1 \%$ of non-spam emails. A new email has just arrived, which does mention "free money". What is the probability that it is spam?
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