基本知识加法原理 ,乘法原理 ,排列数公式 ,组合数公式 ,组合数的性质 (见高中代数课本第九章 ) .2　应用举例排列与组合问题 ,通常要应用加法原理和乘法原理 ,由于这两个原理容易发生混淆 ,我们应特别注意加法原理中每类办法都是相互独立的 ,不受其它类办法的制约 ,而乘法原 The basic knowledge of the principle of addition, multiplication principle, the formula of the number of arrays, the formula of the number of combinations, the nature of the number of combinations (see the ninth chapter of the high school algebra textbook) .2 The application of the example arrangement and the combination of the problems, usually apply the principle of addition and multiplication principle, due to the two The principles are apt to be confused. We should pay special attention to each type of method in the principle of addition is independent of each other, not constrained by other types of methods, and multiplication of the original