A. All seniors and juniors received a survey regarding the upcoming prom. B. A researcher randomly selects several books from the library catalog to count relative frequency of letters. C. A clinic randomly assigns it’s patients willing to participate in the study to either a new treatment or placebo. D. Quality control team removes 20 parts located at the end of the conveyor belt and randomly assigns them either to the stress or temperature test.
I believe the correct answer is B. We are looking at the relative frequency of letters, and you are choosing a random sample of books to count it.
With respect to a random sample, we sample from a population. We like to randomly select a sample from a population. Thank you.