What's the average of 5 MPG and 10 MPG?
The math isn't quite obvious to me, but if you go out camping and get 5 MPG on the way to the campground and turn around and get 10 MGP on the way back, your average MPG won't be 7.5 as you would expe...
Forum Discussion
toedtoes wrote:
Oops - sorry about my math error - not sure how I did that (can I blame my smart phone? :))
But again the the logic of using anything but the original data is faulty. If the gallons used is the same for both trips then the "harmonic mean" of the two MPGs is not what the combined MPG actually is (in that case the arithmetic mean is correct).
So, if you are trying to determine the MPG for an entire trip (as the OP was addressing), then you HAVE to go back to the original data.
No problem, I blame the computer, phone, etc. all the time :)
Again, in my mind, the average MPG and combined mpg are two different things. And the OP has complicated things with a post title and original message that differ. The title is "What's the average of 5mpg and 10mpg?" Given that question and info provided, it is the harmonic mean of 6.67.
The body of original message then relates to the cumulative MPG.
IF you want the cumulative (or combined or total) MPG for whole trip, then the method you described using total gallons consumed and total miles driven must be used. This is not any type of average of multiple MPGs, it is the actual miles per gallon observed.
