I don't get this whole?

Question

20 miles per gallon thing how does that work?

Answer 1

If you buy 1gal you will be able to drive 20miles. If you buy 2gal you can drive 40miles, 60miles with 3gal, and so on...

Alternatively get a more efficient car, e.g. 30mpg, and you will only need to buy 2gal to drive the 60miles.

Higher mpg-value = more miles with the same amount of fuel = less fuel for the same distance = more efficient.

Over here in Europe we use the other approach and count liters per 100km (or gal/mi in non-metric units). Consequently in this system higher values mean higher consumption and therefore less efficiency.