Question: An upper-level sociology class at a large urban university has 120 students, including 34 seniors, 57 juniors, 22 sophomores, and 7 freshmen.

a. Imagine that you choose one random student from the classroom (perhaps by using a ran­dom number table). What is the probability that the student will be a junior?

b. What is the probability that the student will be a freshman?

c. If you are asked to select a proportionate stratified sample of size 30 from the classroom, stratified by class level (senior, junior, and so on), how many students from each group will be in the sample?

d. If instead you are to select a disproportionate sample of size 20 from the classroom, with equal numbers of students from each class level in the sample, how many freshmen will be in the sample?