Consider the random variable X, which has the following probability mass function: f_X(x) = 1/30 x^2, x = 1, 2, 3, 4 Suppose X is in units of mm. What are the units on the variance of X? (mm)^2 mm squareroot mm None of the above Consider the random variable X, which has the following probability mass function: f_X(x) = 1/30 x^2, x = 1, 2, 3, 4 Suppose X is in units of mm. What are the units on the standard deviation of X? (mm)^2 mm squareroot mm None of the above Consider the random variable X, which has the following probability mass function: f_X (x) = 1/30 x^2, x = 1, 2, 3, 4 Suppose X is in units of mm. What are the units on the expected value of X? (mm)^2 mm squareroot mm None of the above