1)If n no. of people sit randomly, they can sit in n! ways.
Out of these k no. of people sit in their alloted seats.
This means that (n-k) no. of people sit randomly.
No. of ways in which they sit in places other than the ones alloted to them

=(n-k-1)(n-k-2)....(1)=(n-k-1)!
Thus,
required probability=(n-k-1)! / n!

PLEAZZZZZ RATE IF CORRECT....