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JEE Main & Advanced Mathematics Permutations and Combinations Question Bank Multinomial Theorem, Number of Divisors, Miscellaneous problems

  • question_answer
    If \[^{n}{{C}_{r}}={{\,}^{n}}{{C}_{r-1}}\] and \[^{n}{{P}_{r}}{{=}^{n}}{{P}_{r+1}}\], then the value of n is

    A) 3

    B) 4

    C) 2

    D) 5

    Correct Answer: A

    Solution :

    The conditions provided that \[n-r=r-1\] Þ \[r=\frac{n+1}{2}\]. So if we put\[n=3\], then \[r=2\] satisfies the conditions.


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