JEE Main & Advanced Mathematics Question Bank Critical Thinking

  • question_answer
    Two persons A and B take turns in throwing a pair of dice.  The first person to through 9 from both dice will be avoided the prize. If A throws first then the probability that B wins the game is                                               [Orissa JEE 2003]

    A)                 \[\frac{9}{17}\]    

    B)                 \[\frac{8}{17}\]

    C)                 \[\frac{8}{9}\]       

    D)                 \[\frac{1}{9}\]

    Correct Answer: B

    Solution :

               The probability of throwing 9 with two dice \[=\frac{4}{36}=\frac{1}{9}\]            \[\therefore \]The probability of not throwing \[9\] with two dice \[=\frac{8}{9}\]            If A is to win he should throw 9 in 1st or 3rd or 5th attempt            If B is to win, he should throw, 9 in 2nd, 4th attempt                 B¢s chances\[=\left( \frac{8}{9} \right)\,.\,\frac{1}{9}+{{\left( \frac{8}{9} \right)}^{3}}.\,\frac{1}{9}+....=\frac{\frac{8}{9}\times \frac{1}{9}}{1-{{\left( \frac{8}{9} \right)}^{2}}}=\frac{8}{17}\].


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