A 2019 study conducted by eMarketer asked 800 US smartphone users whether they had used a food delivery app at least once in the last month. The survey also asked which food delivery app, if any, was used. The survey showed that 16.3% of respondents had used a food delivery app in the last month. Of those that had used one, 27.6% used DoorDash, 26.7% used Grubhub, 25.2% used UberEats, while the rest used another.

(a) What is the sample? What is the intended population?

(b) What are the cases? What are the variables? Classify variables as quantitative or categorical.