Consider students at your college or university with 20,000 undergraduates and 10,000 graduate students enrolled. You are interested in estimating the average summer earnings (April -> August) of undergraduate students. The Registrar provides you with a list of 1000 undergraduate students selected at random. You send them a questionnaire by email and receive responses from $response students.
In order to get more responses for your questionnaire, you decide to wait outside the student building and stop the first 500 students who pass you, of which another $secondresponse students agree to answer your survey.
You read about a similar survey at a neighboring college with 40,000 undergraduate students that used a sample size of 1000 students. You wish to survey your college (with 20,000 undergraduate students) with the same level of precision. To do so you need to decide on the appropriate sample size.
You realize that you need to sample 9xooCZFoFpWHSoNtJzqBipO+42U= students at your college to get the same level of precision as in the larger college.