(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

All athletes at the Olympic games are tested for performance-enhancing steroid drug use. The imperfect test gives positive results (indicating drug use) for 90% of all steroid-users but also (and incorrectly) for 2% of those who do not use steroids. Suppose that 5% of all registered athletes use steroids. If an athlete is tested negative, what is the probability that he/she uses steroids?

2. Relevant equations

3. The attempt at a solution

I did P(defective)=.05

P(Tested defective|defective)=1

P(Tested defective|good)=.02

From there I did P(TD)=(1*.05)+(.02*(1-.05))=.069

(1*.05)/.069=.724 which was wrong. Am I missing a step?

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# Homework Help: Conditional Probabilty

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