Xiao Bai has six toys. How many choices do you have? Choose four of them?

C(6，4)= 15

Suppose your toy is ABCDEF.

4/6 equals 2/6. Because if you take four, there will be two left.

For example, if you choose AB, it means {{CDEF}}. Similarly, there are AC, AD, AE, AF, BC, BD, BE, BF, CD, CE, CF, DE, DF, EF.

{BDEF}{BCEF}{BCDF}？ {ABCD} * * 15。

Extended data:

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 of the two different types of methods are not the same (that is, the classification is not heavy); Any method to accomplish this task belongs to a category (that is, the category will not be revealed).

2. Multiplication principle and step-by-step counting method:

There is no way to finish this task. To complete this task, N steps must be completed continuously. Each step is calculated independently; As long as the methods used in a step are different, the corresponding methods to complete it are also different.