Better gas mileage: A rental company in a large city put a new type of tire with a special tread on a random sample of 50 cars, and the regular type of tire on another random sample of 50 cars. After a month, the gas mileage of each car was measured.

a. Is this a randomized experiment or an observational study?

b. Assume that one of the samples had noticeably better gas mileage than the other. Could this result be due to confounding? Explain.