Problem

1761 England

A condition affects 5\% of a population. A screening test returns positive for 85\% of the people who have the condition, and also returns positive for 5\% of the people who do not.

A person drawn uniformly at random from the population tests positive. The probability that they actually have the condition can be written as \dfrac{m}{n}, where m and n are relatively prime positive integers. Compute m+n.


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Problem Tags: Counting and probability Number theory

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