JCECE Engineering JCECE Engineering Solved Paper-2008

  • question_answer
    Out of \[40\] consecutive natural numbers, two are chosen at random. Probability that the sum of the number is odd, is

    A) \[\frac{14}{29}\]                                              

    B) \[\frac{20}{39}\]

    C) \[\frac{1}{2}\]                                   

    D)  None of these

    Correct Answer: B

    Solution :

    Key Idea In out of \[40\] consecutive numbers, \[20\] are odd and \[20\] are even numbers. Now, the sum of two numbers is odd only when one is odd and other is even. \[\therefore \]Required probability\[=\frac{^{20}{{C}_{1}}{{\cdot }^{20}}{{C}_{1}}}{^{40}{{C}_{2}}}\]                 \[=\frac{20\times 20}{\frac{40\times 39}{2\times 1}}=\frac{20\times 20}{20\times 39}\]                 \[=\frac{20}{39}\]


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