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  3. CET Karnataka Engineering

CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2001

  • question_answer
    If \[{{\,}^{15}}{{C}_{3r}}={{\,}^{15}}{{C}_{r+3,}}\]then r is equal to:

    A)  2                                            

    B)  4

    C)  3                            

    D)  6

    Correct Answer: C

    Solution :

    \[{{\,}^{15}}C{{ & }_{3r}}={{\,}^{15}}{{C}_{r+3,}}\] If \[{{\,}^{n}}{{C}_{r}}={{\,}^{n}}{{C}_{s}},\]then \[r+s=n\] Hence, \[3r+r+3=15\]or \[4r=12\] \[r=\frac{12}{4}=3\]


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