You have the price of 2 different cars one 17,000 the other 23,000 one gets 22mpg and the other 50 mpg at 3.00 a gallon how long will it take until you have spent more on the one that gets 22 mpg than the one that gets 50 mpg?
17,000 + 3 $/gal * (1/22) gal/mi * Mi
= 23,000 + 3 * (1/50) * Mi