Example 1. Select 4 people from 6 boys and 4 girls to participate in an extracurricular interest group. How many ways are there to select them?
(1) At least one boy and one girl participate;
(2) At most 3 boys participate.
Analysis: (1) Consider the selection of 4 students from 10 as the whole. The whole can be divided into two parts: one part is that the selected 4 students include at least one boy and one girl; the other part is that all 4 are either boys or girls, and these two parts are mutually exclusive. Therefore, the solution is: $\mathrm{C}_{10}^{4}-\mathrm{C}_{8}^{4}-\mathrm{C}_{4}^{4}=194$ (ways) 3
(2) The opposite of "at most 3 boys" is "all 4 selected are boys." Together, these two scenarios cover the whole. Thus, the solution is: $\mathrm{C}_{10}^{4}-\mathrm{C}_{0}^{4}=195$ (ways).