There are p (2 1, 21)/(p (6,6) * p (7,7) * p (8,8)) = 349188840 (species).

Description: All boys with 2 1 have P (2 1, 2 1) methods.

The first six categories belong to one category, and each method is repeatedly calculated for p (6,6) times in P(2 1, 2 1) methods.

Seven of them belong to one category, and each method is calculated repeatedly for p (7,7) times in P(2 1, 2 1) methods.

The last eight are a class, and each method is repeated for p (8,8) times in P(2 1, 2 1) methods.

Therefore, 2 1 boys in the class are divided into three different interest classes, with 6 students, 7 students and 8 students in each class.

There are p (2 1, 21)/(p (6,6) * p (7,7) * p (8,8)) = 349188840 (species).

Or ...

Solution 2:

C(2 1，6)*C( 15，7)*C(8，8)= 54264 * 6435 * 1 = 349 188840

Explanation:

6 boys with 2 1 are assigned to a class, and there is a choice method of C(2 1, 6); Then, from the remaining 15 boys, seven students are assigned to a class, and there is a choice method of C (15,7); Then eight of the remaining eight boys are assigned to a class, and there is a C (8,8) selection method.

Therefore, 2 1 boys in the class are divided into three different interest classes, with 6 students, 7 students and 8 students in each class.

There are c (2 1 6) * c (15,7) * c (8,8) = 349188840 (species).

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Solution 3:

C(2 1，7)*C( 14，6)*C(8，8)=349 188840

or

C(2 1，8)*C( 13，6)*C(7，7)=349 188840

……