Here’s the math:
40 miles on a charge, then 50mpg after that. To find out how they came to the 230mpg, we have this:
230miles/gallon = (40 + x) miles / (x/50) gallons
This gives us x = 9, so you get 230 miles per gallon on a 49 mile drive. This (I assume) follows the EPA guidelines for how to test hybrid vehicles for mpg in city driving, otherwise they’d be sticking their necks out to be chopped off by a lawsuit.
But here’s the kicker:
miles 0–40 used no gasoline (see @IchtheosaurusRex for the tradeoff), miles 40–90 used a gallon of gas—that’s 90 miles to the gallon, if we just ignore reality. Miles 90–140 used another gallon of gas (now we’re down to 70 mpg)
At 240 miles, you cross the 60mpg line.
Here’s a graph:
http://bit.ly/7HcgZ