The employee benefits manager of a small private university would like to know the proportion of its full-time employees who prefer adopting each of three available healthcare plans in the forthcoming annual enrollment period. A reliable frame of the university’s employees and their tentative health care preferences are given in P8_25.XLS. 

a. Compute the proportion of the employees in the given frame who favor each of the three plans (i.e., plans A, B, and C).

b. Use Excel to choose a sample of 45 employees stratified by employee classification with proportional sample sizes.

c. Compute the proportion of the 45 employees in the stratified sample who favor each health plan. Compare these sample proportions to the corresponding values obtained in part a. Explain any differences between the corresponding values.