Question 1197425
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I think the conventional understanding of using "every letter once" means to include the duplicated letters.  For this problem, you would permute all 9 letters but then divide by the arrangements of the duplicates:

    9!/(2!*2!) = 362880 / 4 = 90720

OF course, this is also assuming each "word" is just a unique arrangement of letters, and not a dictionary word.

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EDIT:
After re-reading, it is not clear to me.  If each letter must be used "at most once" then why did the problem statement give the duplicate letters?   The formulation of the problem statement could be better.