JEE MAIN - Mathematics (2023 - 25th January Evening Shift - No. 18)

25% of the population are smokers. A smoker has 27 times more chances to develop lung cancer than a non smoker. A person is diagnosed with lung cancer and the probability that this person is a smoker is $$\frac{k}{10}%$$. Then the value of k is __________.
Answer
9

Explanation

Probability of a person being smoker $=\frac{1}{4}$

Probability of a person being non-smoker $=\frac{3}{4}$

$P\left(\frac{\text { Person is smoker }}{\text { Person diagonsed with cancer }}\right)=\frac{\frac{1}{4} \cdot 27 P}{\frac{1}{4} \cdot 27 P+\frac{3 P}{4}}$

$=\frac{9}{10}=\frac{k}{10}$

$\Rightarrow k=9$

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