3. Suppose you roll a fair die and then you roll it again and subtract what you got the second time from what you got the first time. (a) What is the expected value of this random variable? (b) What is its variance and standard deviation? 4. Suppose that X N Poisson(/\\). For each x : 0, 1, 2, 3, . . . , determine Whether there is a corresponding value of A that maximizes the probability mass function at x: p(x) : P({X = x}), and if so, determine that value