Quote:
Originally Posted by RedDevil
Hi Steeve. You can't average mpg like that.
You got 17 mpg over 10 miles; you used about 0.59 gallon for that part.
You got 59 miles going down over 10 miles, that's 0.17 gallon.
So you used 0.78 gallon over the combined 20 miles, that's about 26 mpg, not 38.
If it were 38 over 20 miles then you'd use 0.53 gallon for the total stretch, that's less than the 0.59 gallon for just the uphill part. 0.06 gallon of fuel would have been magically added to your tank on the descent!
There's no simple way to calculate overall mpg other than dividing total distance for each section by the total fuel spent for each section.
Still, 26 mpg is better than 23!
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Yeah the problem is that miles per gallon is an inverse measurement. Consider this extreme example:
I drive up a mountain at 10mpg for 10 miles.
At the top of the mountain I kill my engine and coast down using zero fuel, or infinity miles per gallon.
How do you average infinity with 10?
In actual fact it works out to 20mpg round trip.