Mathematically speaking, the average distribution in the group distribution is divided by the hierarchy of the number of groups because the group does not need a specific position, which is equivalent to not needing it within the group. The distribution needs a position and the change of each position.

The principle of grouping is multiplication principle, which multiplies the number of possibilities or methods. The principle itself has no sequential thinking, which should be kept in mind.

If divided equally, the number of each group is the same, which causes a certain amount of things in the former group to still appear in the latter group, 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.

Definitions and formulas

Definition of arrangement: from N different elements, arbitrarily choose m(m≤n, m and n are natural numbers, the same below) to arrange in a column in a certain order, which is called an arrangement of taking M elements from N different elements; All permutation numbers of m(m≤n) elements from n different elements are called permutation numbers of m elements from n different elements.