RAJASTHAN ­ PET Rajasthan PET Solved Paper-2010

  • question_answer
    The probability that at least one of the events A and B occurs is\[\frac{3}{5}.\] If A and B occur simultaneously with probability\[\frac{1}{5},\]then \[P(\overline{A})+P(\overline{B})\]is

    A)  \[\frac{2}{5}\]

    B)  \[\frac{4}{5}\]

    C)  \[\frac{6}{5}\]

    D)  \[\frac{7}{5}\]

    Correct Answer: C

    Solution :

     \[P(A\cup B)=\frac{3}{4}\] Now,    \[P(A\cap B)=\frac{1}{5}\] \[P(A\cup B)=P(A)+P(B)-P(A\cap B)\] \[\Rightarrow \] \[P(A)+P(B)=P(A\cup B)+P(A\cap B)\] \[\Rightarrow \] \[P(A)+P(B)=\frac{3}{5}+\frac{1}{5}=\frac{4}{5}\] \[\Rightarrow \] \[1-P(\overline{A})+1-P(\overline{B})=\frac{4}{5}\] \[\Rightarrow \] \[-\{P(\overline{A})+P(\overline{B})\}=\frac{4}{5}-2=\frac{-6}{5}\] \[\Rightarrow \] \[P(\overline{A})+P(\overline{B})=\frac{6}{5}\]


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