That would only be a "math problem" if it came with enough numbers to do some calculations.

Oh, wait -- he's probably assuming that the only worthwhile metric in the problem is fuel usage. Well, with that requirement, it's easy. Hell, I've even done the calculations for determining how long it would take to recoup my losses if I bought a motorcycle and used that instead of a car with decent fuel efficiency, given some assumptions about future gas prices, a while ago:

http://sob.apotheon.org/?p=449