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Question: Answered & Verified by Expert
A round table conference is to be held amongst 20 countries. If two particular delegates wish to sit together, then such arrangements can be done in ways.
MathematicsPermutation CombinationJEE Main
Options:
  • A $2 \times(18) !$
  • B $\frac{19 !}{2 !}$
  • C $18 !$
  • D $19 ! \times 2 !$
Solution:
1590 Upvotes Verified Answer
The correct answer is: $2 \times(18) !$
We consider two particular delegates as single unit now 19 units can be arranged around a round table in 18! ways and the two delegates can be arranged mutually in 2 ! ways
Hence the required number of ways is $2 \times(18$ !)

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