1. The variance of a random variable X is defined as the expected value of (X - E(X))^2. The covariance between two random variables X and Y is defined as the expected value of (X - E(X))(Y - E(Y)). 2. Several limits of probabilities (plim rules) are derived from Slutsky's theorem. These include: the plim of a sum of random variables equals the sum of their individual plims; the plim of a constant multiplied by a random variable is that constant multiplied by the random variable's plim; and the plim of a function of a random variable is equal to that function evaluated at the random variable's plim.