在概率论中 ,一个概率很小的事件称为小概率事件 .一般称概率在 0 0 5以下的事件为小概率事件 .根据实际需要 ,人们有时选取 0 .0 1、0 .0 2 5、0 .0 0 5、或其它的很小的数作为小概率 .所谓小概率事件的原则是 :如果一个事件发生的概率很小 ,那么在一次试验中 ,实际上可把它 In probability theory, an event with a very small probability is called a small probability event. Generally speaking, an event with a probability below 0 0 5 is a low-probability event. According to actual needs, people sometimes select 0. 01, 0. 0 2 5, 0. 0 0 5, or other very small number as a small probability. The principle of the so-called small probability event is: If the probability of an event is small, then in an experiment, you can actually