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NDA 2022 Maths · Mathematics · Permutations and Combinations · hard

The number of arrangements of the letters of SUCCESS in which no two S's are adjacent is

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The number of arrangements of the letters of SUCCESS in which no two S's are adjacent is
  1. A. 120120
  2. B. 420420
  3. C. 6060
  4. D. 240240
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Answer: (A) 120120

Arrange U, C, C, E first: 4!2!=12\frac{4!}{2!}=12 ways. This creates 55 gaps; choose 33 of them for the S's: (53)=10\binom53=10. Total 12×10=12012\times10=120. The value 420420 is the unrestricted count.
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