JEE Main & Advanced Mathematics Probability Question Bank Conditional probability bayes theorem

  • question_answer
    If two events A and B are such that \[P({{A}^{c}})=0.3,\,P(B)=0.4\] and \[P(A{{B}^{c}})=0.5,\] then \[P[B/(A\cup {{B}^{c}})]\] is equal to [IIT 1994]

    A)                 \[\frac{1}{2}\]       

    B)                 \[\frac{1}{3}\]

    C)                 \[\frac{1}{4}\]       

    D)                 None of these

    Correct Answer: C

    Solution :

               \[P[B/(A\cup {{B}^{c}})]=\frac{P(B\cap (A\cup {{B}^{c}}))}{P(A\cup {{B}^{c}})}\]            \[=\frac{P(A\cap B)}{P(A)+P({{B}^{c}})-P(A\cap {{B}^{c}})}\]                 \[=\frac{P(A)-P(A\cap {{B}^{c}})}{P(A)+P({{B}^{c}})-P(A\cap {{B}^{c}})}\]\[=\frac{0.7-0.5}{0.8}=\frac{1}{4}\].


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