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How many ways are there to form a sequence of 10 letters from 4 a's, 4 b's, 4 c's, and 4 d's if each letter must appear twice?
So typically I would use the theorem like
16! / 4! 4! 4! 4! (if I was choosing a sequence of 16 and exactly 4 each)
For this example though I would have to lock the spots of 2 of each in place so aabbccdd _ _ and those two extra spots would have 4 choices each, so 4 x 4.
Would it be: (10! / 3! 3! 2! 2!) x 16 ?
Any help would be appreciated!