RAJASTHAN ­ PET Rajasthan PET Solved Paper-2003

  • question_answer
    If\[^{n-1}{{C}_{3}}{{+}^{n-1}}{{C}_{4}}{{>}^{n}}{{C}_{3}},\]then n is equal to

    A)  4                   

    B)  6

    C)  8                   

    D)  7

    Correct Answer: C

    Solution :

     Given, \[^{n-1}{{C}_{3}}{{+}^{n-1}}{{C}_{4}}{{>}^{n}}{{C}_{3}}\] \[\Rightarrow \] \[^{n}{{C}_{4}}{{>}^{n}}{{C}_{3}}\] \[\Rightarrow \] \[\frac{n!}{(n-4)!4!}>\frac{n!}{(n-3)!3!}\] \[\Rightarrow \] \[\frac{n!}{4.3!(n-4)!}>\frac{1}{(n-3)(n-4)!3!}\] \[\Rightarrow \] \[\frac{1}{4}>\frac{1}{n-3}\] \[\Rightarrow \] \[n-3>4\] \[\Rightarrow \] \[n>7\] or \[n=8\]


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