CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2005

  • question_answer
    Two persons A and B throw a die alternately till one of them gets a 3 and wins the game, the respective probabilities of winning, if A begins, are:

    A)  \[\frac{7}{11},\frac{4}{11}\]       

    B)         \[\frac{6}{11},\frac{5}{11}\]

    C)  \[\frac{5}{6},\frac{1}{6}\]           

    D)         \[\frac{4}{7},\frac{3}{7}\]

    E)  \[\frac{1}{2},\frac{1}{2}\]

    Correct Answer: B

    Solution :

    \[\because \] \[p(A)=\frac{1}{6},p(\overline{A})=\frac{5}{6}\] and   \[p(B)=\frac{1}{6},p(\overline{B})=\frac{5}{6}\] Hence, Probability of winning of A \[[=P(E)+P(\overline{E}\cap \overline{F}\cap \overline{E})+\]                                 \[P(\overline{E}\cap \overline{F}\cap \overline{E}\cap \overline{F}\times E)+....\] \[=\frac{1}{6}+{{\left( \frac{5}{6} \right)}^{2}}\left( \frac{1}{6} \right)+{{\left( \frac{5}{3} \right)}^{4}}\left( \frac{1}{6} \right)+.....\] \[=\frac{\frac{1}{6}}{1-{{\left( \frac{5}{6} \right)}^{2}}}=\frac{6}{11}\] Also, probability of winning\[B=1-\frac{6}{11}\text{=}\frac{5}{11}.\]


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