Assume that administrators at a university administered a satisfaction survey to a sample of students. To get a representative sample, they first determined the proportion of students who are freshmen, sophomores, juniors, or seniors. Then, they classified courses as 100, 200, 300, or 400 level (corresponding to freshman through senior level). Then, assuming that most of the students in the 100-level course are freshmen, in the 200-level course are sophomores, and so on, they randomly selected proportional numbers of 100- through 400-level courses in which to administer the surveys. All students in these courses were administered the surveys regardless of their actual class level. However, the results did closely approximate the desired freshman through senior proportions. Which two sampling techniques did the administrators use?