JEE Main & Advanced Mathematics Probability Question Bank Mock Test - Probability

  • question_answer
    A fair die is tossed repeatedly. A wins if it is 1 or 2 on two consecutive tosses and B wins if it is 3, 4, 5 or 6 on two consecutive tosses. The probability that A wins if the die is tossed indefinitely is

    A) 1/3       

    B) 5/21

    C) 1/4                   

    D) 2/5

    Correct Answer: B

    Solution :

    [b] Let P(S)=P(1 or 2) = 1/3 P(F) = P (3 or 4 or 5 or 6) = 2/3 P(A wins) = P[SS or S F SS or S F S F SS or ...) Or (F S S or F S F S S or ...)] \[=\frac{\frac{1}{9}}{1-\frac{2}{9}}+\frac{\frac{2}{27}}{1-\frac{2}{9}}\] \[=\frac{1}{9}\times \frac{9}{7}+\frac{2}{27}\times \frac{9}{7}\] \[=\frac{1}{7}+\frac{2}{21}=\frac{3+2}{21}=\frac{5}{21}\] P(A winning)\[=\frac{5}{21}\], P(B winning)\[=\frac{16}{21}\]


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