Counting Lists With Repetition 1. The problem statement, all variables and given/known data How many ways can you create an 8 letter password using A - Z where at most 1 letter repeats? 2. Relevant equations 3. The attempt at a solution I'm not sure how to attack this problem but first I thought that A-Z considers 26 letters so with no restrictions on passwords we can create 268 passwords. I'm thinking it's 268 - X, where X is a term or a series of terms, but I'm not sure how to determine them, or if this is even the correct setup. Well there are two cases given by the restrictions as follows: A) No letter repeats in which we have a k list without repetition which is given by (n)k = n!/(n-k)! B) One letter repeats in which case I think it's 26*[(n-1)!/(n-k-1)!]. And of course in this case n = 26 k = 8. Is this correct? If not could someone give me a hint?