Question

How many ways are there to distribute n graded homeworks to n students such that none of them gets their own homework back?

Answer 1

Assume N students

Student 1 can get (n-1) papers
Student 2 can get (n-1) papers
Student 3 can get (n-1) papers
etc
Student N can get (n-1) papers

So for N students you can have N(n-1)