Analysis because the math group accounts for one-third of the total number of the three groups, and the two interest groups * * * account for two-thirds of the total number, with a ratio of 3: 4, that is, the model group accounts for 2/3 times 3/(3+4) equals 2/7, and the math group accounts for 2/3 times 4/(3+4) equals 8/3. Because the airplane model is less than math by 4 people and the airplane model is less than math by 8/2 1-2/7=2/2 1, the total number of people in the three groups is 4÷2/2 1 equal to 42 people.

Mathematics accounts for 1/3 of the total.

Model airplane: (1-1/3) ÷ 3/(3+4) = 2/7.

Art proportion: (1-1/3) ÷ 4/(3+4) = 8/21

Total population: 4 ÷ (1/3-2/7) = 84.

Number of students: 84× 1/3 = 28.

Number of model aircraft: 84× 2/7 = 24.

Number of artists: 84× 8/2 1 = 32.