IMathAS-libretexts

Which of the following is an example of stratified sampling?

A sample of 351 people called a radio show to express their opinions about the verdict in the Michael Jackson trial.
In order to assess students' satisfaction with the food establishment on campus, the first 50 students that come out of the student center were interviewed.
A poll asked a random sample of 1,112 adults whether they believe that the use of marijuana for medical reasons should be legalized.
A health educator wanted to study the sleeping habits of the undergraduate students in her university. For her study, the researcher chose a simple random sample of size 150 from each of the classes (150 freshmen, 150 sophomores, 150 juniors, and 150 seniors), for a total of 600 sampled students.
The human resources department of a large bank wanted to assess the job satisfaction of the bank's workers. The department chose four of the bank's branches at random, and used all of the workers in those four branches as the subjects for the study.