題組內容

3. (5% each, totally 15%) Let X and Y be random variables, with the joint PMF $$P_{X,Y}(x,y) = \begin{cases} 1/4 & \text{if } (x,y) = (1,1), (1,2), (2,1), (2,2); \\ 0 & \text{else.} \end{cases}$$

(c) What is the expectation of \( W \)?