Question: Solve the math problem: Each class in a school has 20 students. There are 3 classes. The school as a whole is 50% boys and 50% girls. The first class has 15 girls. The second class has 12 girls. How many boys are in the third class?
Answer: 
The school has 60 students because 3 x 20 = 60
The school has 30 girls because 60 x .5 = 30
The third class has 3 girls because 30 - 15 - 12 = 3
The third class has 17 boys because 20 - 3 = 17