Apparently this is a relatively common interview question to evaluate your reasoning abilities:
With a population of 330 million, and an average age of death of 70, and a driving age of 18, that’s about 74.3% of the population that drives (245.2 million), and probably works a job. Assuming that 80% of these people own a car, that’s about 196 million drivers. If the average car drives 50 miles a day, and the average tank gets 400 miles, then drivers will refuel every 8 days, so every day 24.5 million drivers are refueling. If the average gas station has 8 pumps, and takes 10 minutes to fill a tank, that’s 1,152 cars a day. Let’s assume that these cars all refuel four hours a day on their way home from work. That’s about 200 cars a day. That’s about 122,500 gas stations. If the average tank is 15 gallons, and the cost per gallon is $2.00, then a gas station is averaging about $6,000 per day, or $2,190,000 a year in gas revenue. That sounds about right.