JEE Main & Advanced Mathematics Permutations and Combinations Question Bank Mock Test - Permutations and Combinations

  • question_answer
    There are four letters and four directed envelopers. The number of ways in which all the letters can be put I the wrong envelope is

    A) 8                     

    B) 9

    C) 16                   

    D) none of these

    Correct Answer: B

    Solution :

    [b] There is concept of derangement. The require number is \[4!\left[ 1-\frac{1}{1!}+\frac{1}{2!}-\frac{1}{3!}+\frac{1}{4!} \right]=9\]

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