Final answer:
To find the percentage of students who buy lunch, divide 12 by 15 and multiply by 100, resulting in 80% of the students buying lunch.
Step-by-step explanation:
To calculate what percentage of students buy lunch at school, you divide the number of children who buy lunch by the total number of students in the class and then multiply by 100 to convert it to a percentage. There are 12 children who buy lunch, and there are a total of 15 students in the class. So, the calculation would be (12/15) × 100, which equals 80%. Therefore, 80% of students buy lunch.