Counting the filling stations in the United States

Estimate the number of gas stations in the US.

About 100,000 to 150,000. There are around $280$ million vehicles; if each fills up roughly once a week, that is about $40$ million fills a day. A station with $8$ pumps each serving about $40$ cars a day handles roughly $300$–$400$ fills, so about $40{,}000{,}000/350\approx115{,}000$ stations. The actual count of fuel-selling sites is about $145{,}000$, so the estimate is in the right range.