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Permutations and Combinations question

2023 · 1 Feb · Shift 1 · Q40
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Permutations and Combinations question

2023 · 1 Feb · Shift 1 · Q40

JEE MainMathematicsPermutations and CombinationsNumerical+4 / −1
The number of words, with or without meaning, that can be formed using all the letters of the word ASSASSINATION so that the vowels occur together, is ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 50400

  1. Count the letters in ASSASSINATION

    The word is: A S S A S S I N A T I O N\text{A S S A S S I N A T I O N}A S S A S S I N A T I O N

    Total letters =13= 13=13.

    Their frequencies are:

    • A=3A = 3A=3
    • S=4S = 4S=4
    • I=2I = 2I=2
    • N=2N = 2N=2
    • T=1T = 1T=1
    • O=1O = 1O=1
  2. Identify the vowels

    Vowels are: A,A,A,I,I,OA, A, A, I, I, OA,A,A,I,I,O So total vowels =6= 6=6.

    Consonants are: S,S,S,S,N,N,TS, S, S, S, N, N, TS,S,S,S,N,N,T So total consonants =7= 7=7.

  3. Use the condition that all vowels occur together

    Treat all the vowels as one single block.

    Then the objects to arrange are:

    • 1 vowel block
    • S,S,S,SS, S, S, SS,S,S,S
    • N,NN, NN,N
    • TTT

    So total objects =8= 8=8.

    These 8 objects have repetitions among consonants:

    • SSS repeated 444 times
    • NNN repeated 222 times

    Therefore, number of arrangements of these 8 objects is 8!4! 2!\frac{8!}{4!\,2!}4!2!8!​

  4. Arrange the vowels within the vowel block

    The vowels are: A,A,A,I,I,OA, A, A, I, I, OA,A,A,I,I,O

    Number of distinct arrangements of these 6 vowels is 6!3! 2!\frac{6!}{3!\,2!}3!2!6!​

  5. Multiply both counts

    Total number of required words is 8!4! 2!×6!3! 2!\frac{8!}{4!\,2!}\times \frac{6!}{3!\,2!}4!2!8!​×3!2!6!​

    Now compute: 8!4! 2!=4032024⋅2=4032048=840\frac{8!}{4!\,2!} = \frac{40320}{24\cdot 2} = \frac{40320}{48} = 8404!2!8!​=24⋅240320​=4840320​=840

    and 6!3! 2!=7206⋅2=72012=60\frac{6!}{3!\,2!} = \frac{720}{6\cdot 2} = \frac{720}{12} = 603!2!6!​=6⋅2720​=12720​=60

    Hence, 840×60=50400840 \times 60 = 50400840×60=50400

  6. Final answer

    50400\boxed{50400}50400​

  7. Comparison with stored correct answer

    Stored correct answer = 504005040050400.

    This matches the derived answer.

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