Permutation and Combination


Direction: Find the number of permutations that can be made from the letters of the word 'OMEGA'.

  1. E being always in the middle.











  1. View Hint View Answer Discuss in Forum

    When E is fixed in the middle, then there are four places left to be filled by four remaining letters O, M, G and A and this can be done in 4! ways.

    Correct Option: B

    When E is fixed in the middle, then there are four places left to be filled by four remaining letters O, M, G and A and this can be done in 4! ways.
    ∴ Total number of ways = 4! = 24


  1. Vowels occupying odd places .











  1. View Hint View Answer Discuss in Forum

    Three vowels (O, E, A) can be arranged in the odd places in 3! ways (1st position, 3rd position, 5th position) and two consonant (M, G) can be arranged in the even place in 2! ways (2nd place and 4th place).

    Correct Option: A

    Three vowels (O, E, A) can be arranged in the odd places in 3! ways (1st position, 3rd position, 5th position) and two consonant (M, G) can be arranged in the even place in 2! ways (2nd place and 4th place).
    ∴ Total number of ways = 3! X 2! = 12



  1. Vowels being never together.











  1. View Hint View Answer Discuss in Forum

    Total number of words = 5! = 120
    combining the vowels at one place(OEA) with remaining 2 letters MG, letters can be arranged in 3! ways. Also, three vowels can be arranged in 3! ways.

    Correct Option: B

    Total number of words = 5! = 120
    combining the vowels at one place(OEA) with remaining 2 letters MG, letters can be arranged in 3! ways. Also, three vowels can be arranged in 3! ways
    So, when vowels are together, then number of words = 3! x 3! = 36
    there4; Required number of ways, when vowels being never together =120 - 36 = 84


  1. If 2n + 1Pn - 1 : 2n - 1Pn = 3 : 5, then n is equal to ?









  1. View Hint View Answer Discuss in Forum

    We have If 2n + 1Pn - 1 / 2n - 1Pn = 3/5
    ⇒ 5 x 2n + 1Pn - 1 = 3 x 2n - 1Pn
    ⇒ {5 x (2n + 1)!} / {(n + 2 )!} = 3 x {(2n - 1)!} / {(n - 1)!}

    Correct Option: A

    We have If 2n + 1Pn - 1 / 2n - 1Pn = 3/5
    ⇒ 5 x 2n + 1Pn - 1 = 3 x 2n - 1Pn
    ⇒ {5 x (2n + 1)!} / {(n + 2 )!} = 3 x {(2n - 1)!} / {(n - 1)!}
    ⇒ 10(2n + 1) = 3(n + 2) (n + 1)
    ⇒ 3n2 - 11n - 4 = 0
    ⇒(3n + 1 ) (n - 4) = 0
    ∴ n = 4



  1. The number of different permutations of the word 'BANANA' is ?









  1. View Hint View Answer Discuss in Forum

    There are 3A's 2N's and one B. We have to find the total number of arrangements of 6 letters out of which 3 are alike of one kind, 2 are alike of second kind, thus the total number of words
    = 6! / (3! 2!) = 60

    Correct Option: B

    There are 3A's 2N's and one B. We have to find the total number of arrangements of 6 letters out of which 3 are alike of one kind, 2 are alike of second kind, thus the total number of words
    = 6! / (3! 2!) = 60