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

  • question_answer
    \[{{x}_{1}},{{x}_{2}},{{x}_{3}},...{{x}_{50}}\] are fifty real numbers such that \[{{x}_{r}}<{{x}_{r+1}}\] for \[r=1,2,3....49.\] Five numbers out of these are picked up at random. The probability that the numbers have \[{{x}_{20}}\] as the middle numbers, is

    A) \[\frac{^{20}{{C}_{2}}{{\times }^{30}}{{C}_{2}}}{^{50}{{C}_{5}}}\]

    B) \[\frac{^{30}{{C}_{2}}{{\times }^{19}}{{C}_{2}}}{^{50}{{C}_{5}}}\]

    C) \[\frac{^{19}{{C}_{2}}{{\times }^{31}}{{C}_{2}}}{^{50}{{C}_{5}}}\]

    D) None of these

    Correct Answer: B

    Solution :

    [b] \[n(S){{=}^{50}}{{C}_{5}},n(E){{=}^{30}}{{C}_{2}}{{\times }^{19}}{{C}_{2}}\] \[\therefore P(E)=\frac{^{30}{{C}_{2}}{{\times }^{19}}{{C}_{2}}}{^{50}{{C}_{5}}}.\]


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