Multiple choice

The number of ways in which 21 people can sit around a conference table so that none of them have the same neighbours in any two arrangements is

  1. 20!*2

  2. 21!/2

  3. 21!

  4. 20!/2

  5. 20!
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

It is the correct answer.

Solution : 21 people can sit around a conference table in 20! ways (Fixing the position of 1 person in each case)

But in the above we have included both clockwise and anticlockwise orders that will have the same neighbours.

Hence,the required no. of arrangements are 1/2 * 20!.

It is a correct answer.

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