The financial aid advisor of a university plans to use a stratified random sample to estimate the average amount of money that students spend on textbooks each term. For each of the following proposed stratification schemes, discuss whether it would be worthwhile to stratify the university students in this manner.
a. Strata corresponding to class standing (freshman, sophomore, junior, senior, graduate student)
b. Strata corresponding to field of study, using the following categories: engineering, architecture, business, other
c. Strata corresponding to the first letter of the last name: A– E, F– K, etc.