+275 How many six-digit positive integers can be written using only the digits 1,2 and 3 and have exactly two 1's, two 2's, and two 3's as digits?
I have no idea how to start with this question
1, 1, 2, 2, 3, 3 ==6! / [2!2!2!] ==720 / 8 ==90 - permutations
[(1, 1, 2, 2, 3, 3), (1, 1, 2, 3, 2, 3), (1, 1, 2, 3, 3, 2), (1, 1, 3, 2, 2, 3), (1, 1, 3, 2, 3, 2), (1, 1, 3, 3, 2, 2), (1, 2, 1, 2, 3, 3), (1, 2, 1, 3, 2, 3), (1, 2, 1, 3, 3, 2), (1, 2, 2, 1, 3, 3), (1, 2, 2, 3, 1, 3), (1, 2, 2, 3, 3, 1), (1, 2, 3, 1, 2, 3), (1, 2, 3, 1, 3, 2), (1, 2, 3, 2, 1, 3), (1, 2, 3, 2, 3, 1), (1, 2, 3, 3, 1, 2), (1, 2, 3, 3, 2, 1), (1, 3, 1, 2, 2, 3), (1, 3, 1, 2, 3, 2), (1, 3, 1, 3, 2, 2), (1, 3, 2, 1, 2, 3), (1, 3, 2, 1, 3, 2), (1, 3, 2, 2, 1, 3), (1, 3, 2, 2, 3, 1), (1, 3, 2, 3, 1, 2), (1, 3, 2, 3, 2, 1), (1, 3, 3, 1, 2, 2), (1, 3, 3, 2, 1, 2), (1, 3, 3, 2, 2, 1), (2, 1, 1, 2, 3, 3), (2, 1, 1, 3, 2, 3), (2, 1, 1, 3, 3, 2), (2, 1, 2, 1, 3, 3), (2, 1, 2, 3, 1, 3), (2, 1, 2, 3, 3, 1), (2, 1, 3, 1, 2, 3), (2, 1, 3, 1, 3, 2), (2, 1, 3, 2, 1, 3), (2, 1, 3, 2, 3, 1), (2, 1, 3, 3, 1, 2), (2, 1, 3, 3, 2, 1), (2, 2, 1, 1, 3, 3), (2, 2, 1, 3, 1, 3), (2, 2, 1, 3, 3, 1), (2, 2, 3, 1, 1, 3), (2, 2, 3, 1, 3, 1), (2, 2, 3, 3, 1, 1), (2, 3, 1, 1, 2, 3), (2, 3, 1, 1, 3, 2), (2, 3, 1, 2, 1, 3), (2, 3, 1, 2, 3, 1), (2, 3, 1, 3, 1, 2), (2, 3, 1, 3, 2, 1), (2, 3, 2, 1, 1, 3), (2, 3, 2, 1, 3, 1), (2, 3, 2, 3, 1, 1), (2, 3, 3, 1, 1, 2), (2, 3, 3, 1, 2, 1), (2, 3, 3, 2, 1, 1), (3, 1, 1, 2, 2, 3), (3, 1, 1, 2, 3, 2), (3, 1, 1, 3, 2, 2), (3, 1, 2, 1, 2, 3), (3, 1, 2, 1, 3, 2), (3, 1, 2, 2, 1, 3), (3, 1, 2, 2, 3, 1), (3, 1, 2, 3, 1, 2), (3, 1, 2, 3, 2, 1), (3, 1, 3, 1, 2, 2), (3, 1, 3, 2, 1, 2), (3, 1, 3, 2, 2, 1), (3, 2, 1, 1, 2, 3), (3, 2, 1, 1, 3, 2), (3, 2, 1, 2, 1, 3), (3, 2, 1, 2, 3, 1), (3, 2, 1, 3, 1, 2), (3, 2, 1, 3, 2, 1), (3, 2, 2, 1, 1, 3), (3, 2, 2, 1, 3, 1), (3, 2, 2, 3, 1, 1), (3, 2, 3, 1, 1, 2), (3, 2, 3, 1, 2, 1), (3, 2, 3, 2, 1, 1), (3, 3, 1, 1, 2, 2), (3, 3, 1, 2, 1, 2), (3, 3, 1, 2, 2, 1), (3, 3, 2, 1, 1, 2), (3, 3, 2, 1, 2, 1), (3, 3, 2, 2, 1, 1)] >Total distinct permutations = 90
