JEE Main & Advanced Mathematics Permutations and Combinations Question Bank Self Evaluation Test - Permutations and Combinatioins

  • question_answer
    Number of ways in which 20 different pearls of two colours can be set alternately on a necklace, there being 10 pearls of each colour.

    A) \[6\times {{(9!)}^{2}}\]

    B) 12!

    C) \[4\times {{(8!)}^{2}}\]

    D) \[5\times {{(9!)}^{2}}\]

    Correct Answer: D

    Solution :

    [d] Ten pearls of one colour can be arranged in \[\frac{1}{2}.(10-1)!\] ways. The number of arrangements of 10 pearls of the other colour in 10 places between the pearls of the first colour =10! \[\therefore \] Required number of ways \[=\frac{1}{2}\times 9!\times 10!=5{{(9!)}^{2}}\]


You need to login to perform this action.
You will be redirected in 3 sec spinner