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JEE Main & Advanced Sample Paper JEE Main - Mock Test - 21

  • question_answer
    The number of numbers that can be formed with the help of the digits 1, 2, 3, 4, 3, 2, 1 so that odd digits always occupy odd places, is

    A) 24        

    B) 18   

    C) 12                    

    D) 30

    Correct Answer: B

    Solution :

    [b]: The 4 odd digits 1, 3, 3, 1 can be arranged in the 4 odd places in \[\frac{4!}{2!2!}=6\] ways and 3 even digits 2, 4, 2 can be arranged in the three even places in \[\frac{3!}{2!}=3\] ways. Hence the required number of ways \[=6\times 3=18\]


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