BCECE Engineering BCECE Engineering Solved Paper-2009

  • question_answer
    A man is known to speak the truth 3 out of 4 times. He throws a die and reports that it is a six. The probability that it is actually a six is

    A) \[\frac{3}{8}\]                   

    B)         \[\frac{1}{5}\]                  

    C)  \[\frac{3}{4}\]                  

    D)         \[\frac{1}{2}\]

    Correct Answer: A

    Solution :

    Let E be the event that a six occurs and A be the event that man reports that It is a six. \[\therefore \]\[P(E)=\frac{1}{6},P(E)=\frac{5}{6},P\left( \frac{A}{E} \right)=\frac{3}{4}\] and        \[P\left( \frac{A}{E} \right)=\frac{1}{4}\] Using Bays theorem                 \[P\left( \frac{E}{A} \right)=\frac{P(E).P\left( \frac{A}{E} \right)}{P(E).P\left( \frac{A}{E} \right)+P(E)P\left( \frac{A}{E} \right)}\]       \[=\frac{\frac{1}{6}\times \frac{3}{4}}{\frac{1}{6}\times \frac{3}{4}+\frac{5}{6}\times \frac{1}{4}}=\frac{3}{8}\]


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