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**Counting Lists With Repetition**

## Homework Statement

How many ways can you create an 8 letter password using A - Z where at most 1 letter repeats?

## Homework Equations

## 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 26

^{8}passwords. I'm thinking it's 26

^{8}- 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?

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