1. The problem statement, all variables and given/known data We roll a fair die until we get a three or a four. Z denotes the number of rolls needed. What is the probability that Z >= 3? (replacement assumed) 2. Relevant equations Geometric distribution seems logical here? 3. The attempt at a solution Let p(A) = p(getting a three) = 1/6 and p(B) = p(getting a four) = 1/6. We want p(A U B) = 1/3 (a three OR a four). Correct? Now, we know p(Z >= k) = (1 - p)^(k - 1). Is that enough for this question? I got 4/9.