5.3 Some Rules of Probability
如图所示，AorB是所有蓝色区域，所以P（AorB）=PA+PB，但是若非互斥事件，则不能直接相加：
If you think of the regions as probabilities, the entire region enclosed by the rectangle is the probability of the sample space, or 1. Furthermore, the colored region is P(E) and the uncolored region is P(not E). Thus, P(E) + P(not E) = 1 or, equivalently, P(E) = 1 − P(not E).
如图所示，得到
所以对一不互补的事件的加法公式为：
由图得到：
There are also general addition rules for more than two events. For instance, the general addition rule for three events is
