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排列组合应用题是众所周知的教学难点之一,特别是对于那些“貌异质同”或“形似实异”的应用题的解法,学生常感到无所适从.本文主要想就此提出一些看法和建议。一、“貌异质同”的应用题例1 赵、钱、孙、李、周、吴六个学生排成一列,赵不排在首位,吴不排在末位,有多少种排法? 此题解法甚多,我们考虑用“排斥法”。 6个人的全排列数为6!,其中包括四种情况:
It is one of the well-known teaching difficulties to arrange the combined application questions, especially for students who often find themselves at a loss as to the solution to the problem of “heterogeneity” or “similar reality.” This article mainly wants to put forward some opinions and suggestions. First, the “heterogeneous with the same” application 1 Zhao, Qian, Sun, Li, Zhou, Wu six students in a row, Zhao is not ranked first, Wu is not ranked in the bottom, how many kinds of Pai law? There are many solutions to this problem, we consider using “exclusion law.” The total number of 6 individuals is 6 !, which includes four situations: