Correct. Indeed, they are taking the average of the mpg directly, just the harmonic average (http://en.wikipedia.org/wiki/Harmonic_mean http://en.wikipedia.org/

Correct. Indeed, they are taking the average of the mpg directly, just the harmonic average (http://en.wikipedia.org/wiki/Harmonic_mean http://en.wikipedia.org/wiki/Harmonic_mean) rather than the arithmetic one we are more familiar with.