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UGC-NET | UGC NET CS 2015 Dec – II | Question 32

  • Last Updated : 02 May, 2018

Suppose that from given statistics, it is known that meningitis causes stiff neck 50% of the time, that the proportion of persons having meningitis is 1 / 50000 , and that the proportion of people having stiff neck is 1 / 20. Then the percentage of people who had meningitis and complain about stiff neck is:

(A) 0.01%
(B) 0.02%
(C) 0.04%
(D) 0.05%


Answer: (B)

Explanation: We know Bayes theorem:
P(B|A) = P(A|B) * P(B) / P(A)
P(A) = 1 / 20
P(B) = 1 / 5000
Since, we know that meningitis causes stiff neck 50% of the time i.e. P(A|B) = 0.5
P(B|A) = (0.5 * 1 / 50000) / (1/20)
= 0.02%
So, option (B) is correct.


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