RAJASTHAN ­ PET Rajasthan PET Solved Paper-2009

  • question_answer
    If\[^{n}{{C}_{12}}{{=}^{n}}{{C}_{8}},\]then value of\[^{n}{{C}_{19}}\]is

    A)  1                

    B)  20

    C)  210              

    D)  1540

    Correct Answer: B

    Solution :

     Given, \[^{n}{{C}_{12}}{{=}^{n}}{{C}_{8}}\] \[\Rightarrow \] \[\frac{n!}{(n-12)!12!}=\frac{nQ}{(n-8)!8!}\] \[\Rightarrow \] \[(n-8)(n-9)(n-10)(n-11)\] \[=12\times 11\times 10\times 9\] \[\Rightarrow \] \[n-8=12\Rightarrow n=20\] \[\therefore \] \[^{20}{{C}_{19}}=20\]


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