JEE Main & Advanced Mathematics Probability Question Bank Self Evaluation Test - Probability-I

  • question_answer
    If a and b are chosen randomly from the set consisting of numbers 1, 2, 3, 4, 5, 6, with replacement. Then the probability that \[\underset{x\to 0}{\mathop{\lim }}\,{{[({{a}^{x}}+{{b}^{x}})/2]}^{2/x}}=6\] is

    A) 1/3

    B) 1/4

    C) 1/9

    D) 2/9

    Correct Answer: C

    Solution :

    [c] Given limit, \[\underset{x\to 0}{\mathop{\lim }}\,{{\left( \frac{{{a}^{x}}+{{b}^{x}}}{2} \right)}^{\frac{2}{x}}}\] \[\underset{x\to 0}{\mathop{\lim }}\,{{\left( 1+\frac{{{a}^{x}}+{{b}^{x}}-2}{2} \right)}^{\frac{2}{{{a}^{x}}+{{b}^{x}}-2}\underset{x\to 0}{\mathop{\lim }}\,\left( \frac{{{a}^{x}}-1+{{b}^{x}}-1}{x} \right)}}\] \[={{e}^{\log ab}}=ab=6.\] Total number of possible ways in which a, b can take values is \[6\times 6=36.\]Total possible ways are \[(1,\,\,6),\,\,(6,\,\,1),\,\,(2,\,\,3),\,\,(3,\,\,2).\] The total number of possible ways is 4. Hence, the required probability is \[4/36=1/9.\]


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