# 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? [duplicate]

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!