500
A teacher designs an experiment to test the effects of breakfast on academic success. She splits her class of 24 students into two groups. She tells half of her students to eat breakfast and the other half to not eat breakfast. All the participants are to sleep the same number of hours, get the same amount of exercise, and spend the same amount of time studying. After one month, she measures the academic performance of both groups.
What is controlled in this experiment?
The hours of sleep, amount of exercise, and time spent studying is the same in both groups