Question 1039793
It is a permutation. Let's assum we have four seats and we have 12 students. How many ways these students can be seated. 
One way is 1234, another is 1243, another 1235 and so on. 
The formula for this is n!/(n-r)!
12!/(12-4)! = 12*11*10*9*8!/8!= 12*11*10*9