Tony and Alex are given an opportunity to upgrade any of their cars (interest rates can be ignored). Tony's Toyota that averages 10 miles per gallon (mpg) of gasoline can be traded for a vehicle that averages 15 mpg. Or as another option, Alex's 25 mpg Honda can be traded for a new hybrid vehicle that gets 50 mpg.

If both ladies drive their own cars 12,000 miles per year and their goal is to minimize annual gas consumption, which car should be replaced - Tony's or Alex's? They can only afford for one car upgrade.