EPA Average Fuel Economy 'Test' Question!
 

I found the below Q & A as a footnote (#6, page 8) in an old 1974 EPA paper on Mazda Rotary Engine fuel economy:

Q - "...Suppose a motorist took a trip of 600 miles and used three tanks of gasoline. For the first 200 mile segment he used 10 gallons, in the second 200 mile segment he used 20 gallons, and for the third 200 mile segment he used 18 gallons."

A - The answer is: (a) 13.7 mpg or (b) 12.5 mpg, and why?

REASON: The incorrect answer occurs when arithmetic mean is used; the correct answer occurs when harmonic mean is used.


• Source: EPA document #74-27 -- "A Comparative Study of the Fuel Economy Characteristics of Mazda Rotary Engine Vehicles Versus Conventional Reciprocating Engine Vehicles," April 1974, Test and Evaluation Branch, Emission Control Technology Division, EPA.

The answer is b, as 600 mi/48 gal = 12.5 mpg. I suppose the reason is the incorrect answer uses an average of means, and the correct answer uses the arithmatic mean.

Darrell -- Correct answer, wrong reason.

Move your cursor "over" the blank spaces in the REASON text for the correct reason.

I would love to be able to make the mean of 500 miles at 85 mpg and one mile coasting at 300 mpg. 192,5 mpg ? :p