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

  • question_answer
    Let \[0<P(A)<1\], \[0<P(B)<1\] and \[P(A\cup B)=\] \[P(A)+P(B)-P(A)\,P(B).\] Then                               [IIT 1995]

    A)                 \[P(B/A)=P(B)-P(A)\]

    B)                 \[P({{A}^{c}}\cup {{B}^{c}})=P({{A}^{c}})+P({{B}^{c}})\]

    C)                 \[P{{(A\cup B)}^{c}}=P({{A}^{c}})\,P({{B}^{c}})\]

    D)                 \[P(A/B)=P(A)\]

    Correct Answer: C

    Solution :

     Since \[P(A\cap B)=P(A)\,P(B)\]            It means \[A\] and \[B\] are independent events so \[{{A}^{c}}\] and \[{{B}^{c}}\] will also be independent. Hence            \[P{{(A\cup B)}^{c}}=P({{A}^{c}}\cap {{B}^{c}})=P({{A}^{c}})\,P({{B}^{c}})\] (Demorgan?s law)            As \[A\] is independent of \[B,\] hence                 \[P(A/B)=P(A)\],          \[\{\because \,\,\,P(A\cap B)=P(B)P(A/B)\}\].


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