Permutation and combinations

Question

A classic counting prdoblem is to determine the number of ways that the letters of " personnel" can be arranged. Find that number

Answer 1

There are 9 letters which can be arranged in 9! ways

We have 2 e's, 2 n's. So we must divide the 9! by 2! (because of the repeated e's) and 2! (because of the repeated n's ). So 9! / (2! 2!)