Problem 1
The variable "favorite style of sweatshirt" is a qualitative variable instead of a quantitative one. This is because the categories "hoodie", "pullover" and "zip-up" are not quantitative in nature. They are simply labels or names. Yes we can assign a frequency tally for each one, which is likely what she's doing, but that's a slightly different story from what your teacher is asking.
An example of a quantitative variable is "height". This variable can take on any positive numeric value, within realistic reason of course. Theoretically there are infinitely many possible height values if we allow as much precision as we want. Even in a more finitely restricted space, we still have a lot of values to work with. We don't consider each number a different label or category or class. It's just a number. So that's what makes "height" a quantitative variable.
Keep in mind that just because you have a number, doesn't mean it's automatically quantitative. A phone number or a basketball player jersey number are two examples of numbers that are labels. We cannot add up a bunch of phone numbers to get something meaningful. Ask yourself "can I do math operations on these numbers?". If the answer is "yes", then you have quantitative data. Be careful to ask this question for any kind of data you have. Going back to Dyani's data, the category names cannot have math operations applied to them, so that's more evidence we're not dealing with quantitative data.
In short, Dyani has qualitative data instead of quantitative data. Specifically, she has nominal data because each label can be thought of as a name. There is no order to each choice, which means the data is not ordinal.
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Problem 2
The answer to this question is found at the top, in the very first sentence. She wants to know what the most common car is. The population is the set of all student drivers at that school. Let's say there are 400 students who drive to school. That would mean the population would be those 400 people.
Because it's likely too time consuming to survey every member of the population, a sample is used instead to make the best estimate of what the population is. So this is what she's doing when she asks every 10th student to take part of the survey. This is known as systematic sampling because there's a pattern or rule to her choices. This form of sampling can be fairly unbiased assuming that she does this on various different days to get a good snapshot. If she only did it on one day, then it could be likely that some students skipped school or some were out sick. The more she samples, the better look she'll have at the population.
