[ric2b]

From: https://www.popularmechanics.com/cars/a12367/4324986/

"Quick, which is better: Replacing an 18-mpg car with a 28-mpg one, or going from a 34-mpg car to one that returns 50 mpg? Researchers at Duke University say that drivers find it easier to select the right answer when efficiency is expressed as gallons per 100 miles (g/100m).

So 18 mpg (or 5.5 g/100m) versus 28 mpg (3.6 g/100m)--an increase of 10 mpg--represents a 52 percent reduction in consumption.

If you trade in a car rated at 34 mpg for one rated at 50 mpg, its a 16-mpg improvement, so we ought to see those gas card bills plummeting, right? Actually, after a minute's worth of math, you'll get 2.9g/100m in the 34-mpg car and 2g/100m in the 50-mpg car--only half as big a gain as the original scenario. "