1. The problem statement, all variables and given/known data If X is a discrete random variable with mean u = 12 and variance = 9, use Chebyshev's Theorem to find an upper bound for P(X = 21). 2. Relevant equations 3. The attempt at a solution Now, I'm not sure about this since there are different upper bounds, right? P(|21 - 3k < 21 < 21 + 3k|) ≤ 1 / k^2. We solve the inner inequality and we get -k < 3 < k. To find an upper bound, do we simply take a value k > 3? And an unrelated question (just not to make another thread): Let A and B be two events with P(A) = 3/4 and P(B) = 1/3. Explain why 1/12 ≤ P(A intersection B) ≤ 1/3. How do we approach this exactly?