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北师大版《数学》九年级(上)第六章“频率与概率”讲授了利用树状图法或者列表法求解“先后取两张牌”型概率题,这类型题目的主要特征为取牌有先后顺序.作为拓展,教材也给出了“同时取两张牌”型概率题,这类型题目的主要特征为取牌没有先后顺序和同一张牌不可同时重复出现.然而在解题过程中,学生往往会掉进这两个陷阱里面去,有时教师也会出现错误,教师间也会出现争论.为此,笔者归纳出“同时取两张牌”型概率题的两个典型错误,下面将就这两个典型错误展开阐述.
Beijing Normal University version of “Mathematics” ninth grade (on) sixth chapter “frequency and probability ” taught the use of dendrogram or list method to solve “two cards in succession ” probability problem, this type of topic The main feature is the order of taking cards .As a development, the textbook also gives the “take two cards at the same time” type probability questions, the main features of this type of title is the absence of the order of cards and the same card can not be repeated at the same time However, during the problem - solving process, students often fall into the two traps, and sometimes teachers will make mistakes and disputes among teachers.Therefore, the author concludes that “taking two cards at the same time” Probability questions of the two typical mistakes, the following two typical mistakes will be elaborated.