Find a formula for p(x) = P(X=x) .... So I have a test tomorrow and this question is in a list of review questions and I'm having trouble remembering where the mu fits into the formula. Any help would be greatly appreciated :) Question: Suppose that X is a random variable with just two possible values a and b. For x = a and b find a formula for p(x) = P(X = x) in terms of a, b and mu = E(X).