Which of the following is a quantitative variable?

A quantitative variable is one that can be measured numerically and expresses a measurable amount. Mileage of a car fits this definition because it represents a numerical value that indicates the distance a car has traveled, which can be expressed in units such as miles or kilometers. This measurement allows for a variety of mathematical operations to be performed on the data, such as calculating averages or determining frequencies.

In contrast, the other options involve categorical data rather than quantitative data. The existence of a charge account or being a college graduate represent binary or categorical outcomes that cannot be quantified numerically. Similarly, identifying the manufacturer of a cell phone is also categorical, as it represents distinct categories (brands) without any inherent numerical value associated with them. Thus, mileage stands out as the only option that provides numeric measurements, confirming its status as a quantitative variable.