1, the principle of grouping is multiplication principle, which multiplies the number of possibilities or methods. The principle itself has no sequential thinking, so remember this! (The multiplication principle is similar to the sign-in grouping, and the grouping itself is also a sign-in grouping. )

2. If it is divided equally, the number of each group is the same, which leads to: a certain amount of things in the former group can still appear in the latter group (please understand this sentence carefully), which is equivalent to putting things in the former group behind, that is, the members of the group remain unchanged but appear in different groups, which is called order change; The possibility or number of methods produced by this order change is the factorial of the group number. This is also the order problem caused by the multiplication principle in average grouping, but it does not mean that the multiplication principle itself has the order problem! !

3. For non-uniform grouping, the members of the previous group can't just appear in the later group, so there is no order problem.