試題詳解

293. A company provides disability benefits to its employees. There are only two possible benefits: partial disability, costing the company 40, and total disability, costing the company 200. The company employs a number of married couples.
Let (X,Y) denote the company's disability costs for a randomly selected employed married couple. The joint probability function for (X,Y) is:

 Calculate the standard deviation of the total disability cost X + Y for the married couple.
(A) 12.3
(B) 13.8
(C) 15.7
(D) 16.6
(E) 19.8