JEE Main & Advanced Mathematics Probability Question Bank Use of permutations and combinations in probability

  • question_answer
    Three integers are chosen at random from the first 20 integers. The probability that their product is even, is           [Kurukshetra CEE 2002]

    A)            \[\frac{2}{19}\]                       

    B)            \[\frac{3}{29}\]

    C)            \[\frac{17}{19}\]                     

    D)            \[\frac{4}{19}\]

    Correct Answer: C

    Solution :

                       The total number of ways in which 3 integers can be chosen from first 20 integers is \[^{20}{{C}_{3}}.\] The product of three integers will be even if at least one of them is even.            \[\therefore \]Required probability = 1 ? Probability that none is even                                              \[=1-\frac{^{10}{{C}_{3}}}{^{20}{{C}_{3}}}=1-\frac{2}{19}=\frac{17}{19}.\]


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