Identify which of these types of sampling is used: simple random, stratified, systematic, or convenience. 49 students are selected at random from the Sophomore class, 39 from the Junior Class, and 48 from the Senior Class. Systematic A sample consists of every 20th student who leaves the library. Convenience A pollster uses a computer to generate 500 random numbers, then interviews the voters corresponding to those numbers. A researcher interviews 19 work colleagues who work in his building Stratified Simple Random