Question 1091994

By repeated they mean if you choose, say, the letter A then you can still choose a letter A for the 2nd letter.   
(And of course, the same logic applies to the digits, if a number is chosen and can be repeated, then you can choose that same number again).   Note that some problems will use the term "with replacement" to indicated "repeats allowed."
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So for the no repeats allowed case:  you have 26 choices of letters for the first one, then 25 choices for the 2nd.   
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You probably have enough info now to solve it.  Send a message if you want me to check your answer.
Hope this has helped you!
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