Update...

Okay I just crunched pencil to paper and the MPG on our first tank was between 36.2 and 36.9 mpg depending on whether or not the tank was properly zeroed out. It had 12 miles on it when we bought it... and I think it was zeroed for 36.9 mpg. If that is the case, that's not bad given my nephew's driving. I think we will be able to get much better mpg since neither or us are speed demons.

The 38 mpg was the Altima hybrid display number.