Question

the ternary string 2122010 consists of exactly 2 zero's, 2 one's and 3 two's; another ternary string meeting these conditions is 0021221. How many ternary strings are there with exactly 3 zero's, 3 one's and 3 two's

Answer 1

This is just the number of permutations of the set {0, 0, 0, 1, 1, 1, 2, 2, 2}. There are 9 elements in the set, so there are 9! = 362,880 possible ternary strings with exactly 3 each of 0, 1, and 2.