A person is selected at random from a population that has the following characteristics

A person is selected at random from a population that has the following characteristics:

65% of the people are men; the others are women

12% of the men are smokers

7% of the women are smokers


Find the chance that the selected person is a non-smoker, given that the person is a man.

(Decimal answer, please, correct to four decimal places.)

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What have you tried? conditional probability? –  Ehsan M. Kermani Apr 19 '13 at 17:51

2 Answers

Hint: Read the second line carefully. Do not be distracted by the women.

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It seems that the question might be: "Find the chance that the selected person is a man, given that the selected person is a non-smoker". (task for Bayes' theorem using) –  Oleg567 Apr 19 '13 at 18:06
True, the real question might be that. Or perhaps that question will be asked later in the exercises. In probability/statistics courses directed to people outside the sciences, the pace is often very gentle. –  André Nicolas Apr 19 '13 at 18:12

You know that the person is a men and the chance the he is smoking is 12%. Assuming that smokers and non-smokers form a partition of men, $p(smoker)+p(non-smoker)=1.$ Substitute $p(smoker)$ by it's value, $0.12, p(non-smoker)=1-0.12=0.88=88$%

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Thanks Moray95, it was good, if you read again and again the Q, you understand some thing different. –  user73408 Apr 19 '13 at 19:00