排列组合问题类型繁多、方法丰富、富于变化,稍不注意,极易出错.本文选择一些在教学和考试中学生常见的错误进行正误解析,以飨读者.一、没有理解两个基本原理出错排列组合问题基于两个基本计数原理,即加法原理和乘法原理,故理解“分类用加、 Arrange the combination of various types of problems, rich in methods, rich in change, a little careless, error-prone.This article chooses some errors in teaching and test students common mistaken analysis, in order to readers.One, did not understand the two basic principles of error The combinatorial problem is based on two basic counting principles, namely the additive principle and the multiplication principle, so to understand ”classification plus,