独立事件的组合概率

P(H)= 1/2

P(T) = 1/2

Two way to figure out the result

1. 枚举出所有的情况

P(H,H) = 1/4 (H,H ; H,T ; T,H ; T,T)

2. 每次事件都是独立的，计算独立事件都发生的概率

P(H,H) = P(H) P(H) = (1/2) (1/2) = 1/4

P(T,H,T) = P(T) P(H) P(T) = (1/2) (1/2) (1/2) = 1/8