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
Actually I have the answer of the first part and it is (n-k-1)! / (2k4) but I don't know how it has come.I agree with you and I think some other cases in the problem have to be considered as well.Well please try!!!!!!!!!!!!!!!!!!!! for the ii) and iii).