An urn contains 2 green balls, 2 red balls, 1 yellow ball, and 1 white ball. You draw 6 balls, with replacement. What is the probability that there is at least one color repeated exactly twice?
Hint - use inclusion-exclusion principle.
My attempt - I generally know how the hint works and I think I get a sense of how to choose/count balls using "with replacement." Having said this, what does the question mean by "repeated exactly twice"? Is it trying to say one color is meant to occur twice, or thrice?