What is the principle of exclusion?

The analysis is based on the basic formula of binary set principle: A+B-AB all satisfied = Total -AB all satisfied. The number of people participating in the national competition is 240× = 140, and the number of people participating in the two-level competition is 240× =60. The number of people who are not satisfied with both is 0, so we can get 140+x-60=240, and get x= 160. So, the choice of this question is A.

(2) Three sets of exclusion principles.

The concept is similar to that of the two sets, except that a third thing, Class C, is added, and the formula used is different when the repeated part is removed. The basic formulas of the three groups are as follows:

V formula 1: V formula 2: Example 2 A company recruits employees, and each person can apply for up to two positions according to the regulations. Results A total of 42 people applied for positions A, B and C, and the number of applicants was 22, 16 and 25 respectively, among which 8 people applied for positions A and B at the same time and 6 people applied for positions A and C at the same time. So, Baoyi and C opened positions at the same time.

A.7 people B. 8 people

C.5 people D. 6 people

Answer a

This paper analyzes the typical three-set standard including exclusion principle, and directly solves it according to the formula. Assuming that the number of people at Baoyi and C is X, the equation is obtained according to the formula: 42-0 = 22+ 16+25-8-6-X+0, and x=7. Therefore, the choice of this question is a.

Note: Just find the corresponding position of each item in the formula in the stem.

Example 3 An enterprise investigated users' habit of obtaining information from the Internet, and the questionnaire recovery rate was 90%. Among the respondents, 179 people used search engines to get information, 146 people got information from official website, and 246 people got information from social networks. At the same time, 1 15 people used these three methods, 24 people used two of them, and 52 people did not use these three methods. How many questionnaires were sent out in this survey? ( )

3 10

C.390 D. 4 10

Answer d

Analysis of the direct application of the typical formula of three sets inclusion principle, only the number of people who meet two conditions is known, so the second formula of three sets must be adopted in this question. Assuming that X questionnaires are recovered, the equation is obtained according to the formula: