C represents the number of combination methods, such as c (3 3,2), which means that two methods are selected from three objects, and there are three methods in total, namely, A, A, C and B (when the three objects are different).

2, the calculation formula of a:

A represents the number of arrangement methods, for example, n different objects, M (m

Two common basic counting principles of permutation and their applications;

1, addition principle sum classification counting method;

Each method in each category can accomplish this task independently. The specific methods in two different categories are different from each other (that is, the classification is not heavy), and any method to accomplish this task belongs to a certain category (that is, the classification is not leaking).

2. Multiplication principle and step counting method:

One method of any step can't complete this task, and this task can only be completed by continuously completing these n steps, and the counting of each step is independent of each other. As long as the methods used in one step are different, the corresponding methods to complete this matter are also different.