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.
If it is a MCQ, I would choose D. as my interpretation of "random selection procedure" is to ensure that each respondent has the same chance of being selected into the sample.
in D, the goal is to have a sample test whether the products are produced according to the expected value.
A = to me is an intended selection
B = to me is the making of observation so as to make a conclusion on the frequency of letters used in the book.
C = to me the purpose of the selection is not clear