在我们学习用列表法或画树状图法求概率时发现,这两个方法都可以列出所有可能的结果,而树状图对于选取不重复、不放回的概率题能不重不漏、更加简洁方便地表示,并且列表法只能适合于两步完成的事件,而树状图法却适合两步或两步以上完成的事件,所以用好树状图可以为我们解决概率题做好导航,达到一通百通的目的.例1(2014·淮安)班级准备召开主题班会,现从由3名男生和2名女生所组成的班委中,随机选取两人担任主持人,求两 When we study the probability of using the list method or the dendrogram, we find that both methods can list all the possible results, and the dendrogram can not miss the probability of non-repetition and non-repetition , More concise and easy to represent, and the list method can only be suitable for the two-step event, and the dendrogram method is suitable for two or more steps to complete the event, so make good use of the dendrogram can solve the probability problem Good navigation, to achieve the purpose of a pass.Example 1 (2014 · Huai’an) class prepare for thematic class meeting, now from the three boys and two girls from the class committee, randomly selected two as the host, seeking two