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JEE Main & Advanced Mathematics Permutations and Combinations Question Bank Definition of permutation, Number of permutations with or without repetition, Conditional permutations

  • question_answer
    The sum of the digits in the unit place of all numbers formed with the help of 3, 4, 5, 6 taken all at a time is [Pb. CET 1990]

    A) 18

    B) 432

    C) 108

    D) 144

    Correct Answer: C

    Solution :

    Required sum\[=3\ !(3+4+5+6)=6\times 18=108\]. [If we fix 3 of the unit place, other three digits can be arranged in \[3\ !\] ways similarly for 4, 5, 6.]


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