Ok a couple of things:

First off MPG is Miles PER Gallon. Any time you have anything PER any second thing you always divide the first thing by the second thing. Miles PER Gallon is Miles / Gallons.

Second, I bet someone does get 50 MPG for an entire tank eventually. 50 MPG would be about 30% higher than EPA which is not much of a strech for a hypermiler. My current tank is running aroud 80 MPG which is about 60 percent higher than the EPA combined rating of 48.5.