TU Wien:Diskrete Mathematik für Informatik UE (Gittenberger)/Übungen WS13/Beispiel 44

Find the number of ways to place n rooks on an n x n chess board such that no two of them attack each other

Solution

n!

nxn (n-1)x(n-1) ... 1x1 possibilites we cant distinguish between the n rooks --> divide by n!