The number of exercise books is fixed, so the number of people distributed is inversely proportional to the number of books each person gets.

So the number of girls * 15 = the number of boys * 10.

Number of girls: Number of boys = 10: 15 = 2: 3.

Class size: Number of boys = (2+3): 3

The class size is 5/3 times that of boys, so the class size is 3/5 times that of only students.

Number of copies of each class = 10 * 3/5 = 6.

0.5 * 6 = 3 yuan for the first place in the class.