試題詳解

76. A car dealership sells 0, 1, or 2 luxury cars on any day. When selling a car, the dealer also tries to persuade the customer to buy an extended warranty for the car. Let X denote the number of luxury cars sold in a given day, and let Y denote the number of extended warranties sold.
P[X = 0, Y = 0] = 1/6
P[X = 1, Y = 0] = 1/12
P[X = 1, Y = 1] = 1/6
P[X = 2, Y = 0] = 1/12
P[X = 2, Y = 1] = 1/3
P[X = 2, Y = 2] = 1/6
Calculate the variance of X.
(A) 0.47
(B) 0.58
(C) 0.83
(D) 1.42
(E) 2.58