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    Question

    Nine boys have to stand in a circle. In how many ways they are to be stand on the circumference of circle?

    A 20450 Correct Answer Incorrect Answer
    B 20280 Correct Answer Incorrect Answer
    C 20340 Correct Answer Incorrect Answer
    D 20160 Correct Answer Incorrect Answer

    Solution

    Any boy may be stand on any place so there is no difference in clockwise and anticlockwise direction here.   Requirement permutations = 1/2 × (n - 1)!   => 1/2 × (9 - 1)!   => 1/2 × 8!   => 20160

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