[M_a_t_t]

If you only wanted the average for the trip/data recorded same you probably could have used the averages. Just use the average flow rate and average speed and the overall time to calculate total. So if you averaged 35.87 mph for one hour and 12.75 lb/hr (2.023 gal/hr) then you would get the average for the data. Which would be 17.7 mpg

Sorry, I just realized that after re reading everything.

If you do it the other way you would be able to see how your fuel economy was fluctuating and with some more math you could tell when and where you were getting the best fuel economy