Fermi estimate: gallons of gasoline consumed in the US per day?

How to answer

~330M people, ~2×10^8 light vehicles driven daily, ~30 mi/day at ~25 mpg = 1.2 gal/car/day. 2×10^8 × 1.2 ≈ 2.4×10^8 gal/day. True figure ~3.7×10^8 gal/day (~9M barrels), so within ~1.5× — solid. State assumptions explicitly and keep to 1 sig fig.

Key idea: Carrying false precision and not stating assumptions. Round aggressively to 1 sig fig and reason out loud.