2-15. A silver coin is flipped twice. The sample space is denoted by S1 and S2 respectively. S1 = {HH, HT, TH, TT} where, H denotes the head and t denotes the tail. The occurrence of coming head and occurrence of coming tail are independent events. P(H) = P(T) = ½ a) P( a head on the first flip) = 2/4 = 1/2 b) P ( a tail on the second flip given that the first toss was a head) = P(T|H) = P( H and T)/ P(a tail on the second flip) = (¼)/ (½) = 1/2