 In this video we provide the solution to question number six for practice exam number four for Math 1030, in which case we have the following situation. A study is done to determine the average tuition for San Jose State undergraduate students paid per semester. Each student in the following samples is asked how much tuition he or she paid for the fall semester. There's four groups that they're put into, either freshmen, sophomores, juniors, or seniors. And we're going to number them one, two, three, four. A random number generator is used to pick two of those numbers. So a random number generator could pick something like one and two or one and three or two and four or something like that. And so all students in those two years are going to be in the sample. What type of sampling is this? Well, this is an example of a cluster sampling because we put all of the students into a groups and then random groups are decided and then you're going to sample everyone in that. So that's the basis of cluster sampling. Now, if I were to evaluate this, there are some issues I have with this cluster sample because clusters should be representative groups of the whole population. And the fact that you put them by this qualitative information of freshmen, sophomore, junior, senior means that if I only choose the freshmen and sophomores, if those are the two numbers that might not be representative of what the tuition juniors and seniors do. I would have some arguments on how this cluster sampling is done, but nonetheless, this is cluster sampling. Now, some of us might be tempted to think that this is stratified because the groups of freshmen, sophomore, junior, seniors, these definitely do feel like strata that you would do. But a stratified sampling would be to take the same number of freshmen, sophomore, junior, seniors, but that's not what they did here. So this is not a stratified. It's not systematic because systematic would be like, oh, we're going to list all of the students and then we're going to grab everyone 100 students or something like that. It's not systematic. It's definitely not random. I mean, it might be tempted that the groups were chosen randomly, but a simple random sampling is when you choose the members of the population randomly. So that's not the case either. It's not convenient sampling that be like, I'm going to talk to everyone at the student center and see what they pay. Never do convenient sampling. And then lastly, it's not a quota either because we don't have any expectation of how many freshmen, sophomore, junior, seniors we'd get there. So this is definitely a cluster sampling, even if it's not a really good cluster sampling.