Identify which of these types of sampling is used: cluster, convenience, simple random, systematic, or stratified. Justify for full credit.
(a) A STAT 200 professor wants to estimate the study hours of his students. He teaches two sections, and plans on randomly selecting 10 students from the first section and 15 students from the second section.
(b) A STAT 200 student is interested in the number of credit cards owned by college students. She surveyed all of her classmates to collect sample data.
(c) The quality control department of a semiconductor manufacturing company tests every 100th product from the assembly line.
(d) On the day of the last presidential election, UMUC News Club organized an exit poll in which specific polling stations were randomly selected and all voters were surveyed as they left those polling stations.