元素分组问题是排列组合中的难点、易混合,应引起我们对它的重视.现在就此类问题的几种易混情形予以辨析.1.非平均分组在非平均分组中,无论是分配到指定位置(即有组名),还是不分配到指定位置(即无组名),其分组的方法种数相同.例1 把12个人分成如下三组,分别求出以下 The problem of element grouping is difficult and easy to mix in permutations and combinations, which should cause us to attach importance to it. Now we will distinguish several miscellaneous situations of such problems. 1. Non-average groupings in non-average groupings, whether assigned to specified The location (that is, there is a group name), or is not assigned to the specified location (that is, no group name), the method of grouping the same number of species. Example 1 The 12 individuals are divided into the following three groups, respectively, to find the following