A principal wants to survey 100 students about their favorite subject. She asks the first 100 students who walk into the school to fill out a questionnaire. Is this a random sample or a biased sample? Justify your response.

This is a random sample. The principle did not ask a specific group of people for their answer, which could have resulted in a biased sample. Instead the principal asked the first 100 people that walked into the school, which is completely random.