J & K CET Engineering J and K - CET Engineering Solved Paper-2013

  • question_answer
    If S is the sample space and \[P(A)=\frac{1}{3}\,P(B)\]and \[S=A\cup B,\] where A and B are two mutually exclusive events, then \[P(A)\] is equal to

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

    B)  \[\frac{1}{2}\]

    C)  \[\frac{3}{4}\]

    D)  \[\frac{3}{8}\]

    Correct Answer: A

    Solution :

    Hence, A and B are mutually exclusive events.. \[P(A\cap B)=0\] Also,   \[S=A\cup B\] \[\therefore \]  \[P(\bar{A}\cup B)=1\] \[P(A\cup B)=P(A)+P(B)-P(A\cap B)\] \[\Rightarrow \] \[1-\frac{1}{3}P(B)+P(B)-0\] \[\Rightarrow \] \[1=\frac{4}{3}P(B)\Rightarrow P(B)=\frac{3}{4}\] \[\therefore \] \[P(A)=\frac{1}{3}P(B)=\frac{1}{3}\times \frac{3}{4}=\frac{1}{4}\]


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