Toss a fair die 12 independent times. Let Xi denote the number of times i occurs, i = 1,2,3, 4,5,6. (a) What is the joint pdf of X1, X2, ..., X6? (b) Find the probability that each outcome occurs two times. (c) Obtain P( X; = 2) . (d) Are Xi, X2, ..., X6 mutually independent