Car A gets 25 miles per gallon and costs $13,000. Car B is a hybrid that gets 45 miles per gallon, but costs $25,000. Assume you drive 15,000 miles per year and that gas will cost $4 per gallon for the foreseeable future. How many years will it take for Car B's better fuel economy to outweigh its higher initial cost?

The initial cost of car B is 25,000.

The cost of fuel consumed in n years by car B is 
     [tex]=n\times \frac{15000\:miles}{year}\times \frac{1\:gallon}{45\:miles}\times \frac{4\:dollars}{gallon}[/tex]

Equate the initial cost to the cost of fuel
     [tex]25000=n\times \frac{15000\:miles}{year}\times \frac{1\:gallon}{45\:miles}\times \frac{4\:dollars}{gallon}[/tex]

     [tex]25000=\frac{4000n}{3}[/tex]

     [tex]n=\frac{25000\left(3\right)}{4000}[/tex]

     [tex]n=18.75[/tex]

It will take 18.75 years for Car B's better fuel economy to outweigh its higher initial cost.