Here's my first 5205.2 miles of driving:
Gallons Miles Tank's MPG
9.423 297.50 31.57169
7.938 273.90 34.50491
9.566 332.90 34.80033
9.092 298.70 32.85306
9.195 309.00 33.60522
8.923 324.40 36.35548
8.469 315.80 37.28894
8.799 316.80 36.00409
8.613 323.00 37.50145
8.421 313.10 37.18086
9.405 345.20 36.70388
9.002 352.70 39.18018
9.980 386.40 38.71744
8.287 324.00 39.09738
8.845 335.30 37.90842
9.036 356.50 39.45330
Just adding up the total gallons and miles gives: 142.9940 gallons over 5205.200 equals 36.40153 miles per gallon.
Finding the mean mpg of the fillups listed above gives 36.42042 mpg with an error on the mean of 0.5751547.
Either way it looks like my lifetime average is 36.4+-0.6 mpg.
I'd love to hear what the 40+ mpg group is doing to get that kind of
lifetime mileage.