Topic: Choose three members from the five members of the class committee to be members of class study, recreation and sports respectively. If two of them can't serve as recreation committee members, there are different ways to choose.

The solution 1 is classified first and then divided into steps.

(1) Neither Party A nor Party B has been selected. Assign work to the other three people, and the method number is a (3,3) = 6;

(2) Party A and Party B only choose one. First, two people are selected from the remaining three people, then 1 person is selected from the selected two people as the cultural and recreational committee member, and finally, A (or B) and the remaining 1 person are assigned jobs. The method number is 2c (3,2) c (2,1) a (2,2) = 24;

(3) Choose both sides. First, choose 1 person from the other three people as the cultural and entertainment committee members, and then assign the work to Party A and Party B. The method number is C(3,1) a (2,2) = 6;

The total number of methods is a (3,3)+2c (3,2) c (2,1) a (2,2)+c (3,1) a (2,2) = 36.

Solution 2 Negative thinking.

Choose 3 out of 5 people, the method number is a (5,3) = 60, the method number of Party A as a cultural and entertainment committee member is a (4,2) =12, and the method number of Party B as a cultural and entertainment committee member is a (4,2) =12, so the method number is a (5,3)-.