How do you answer when a stranger asks about MPG?

I just answer honestly. I love people who say they get 20 MPG towing but formulas for diesel fuel Lb/Hp tell the real story and after running Class 8 trucks over 3 million miles I can tell you a Peterbilt with a 500 Hp CAT, loaded from Balt-SEA-BALT over 425,000 miles including empty miles averages 6.5 Westbound and 7.1 eastbound. This is because the winds across the US are either from the SW or North a good part of the time and you climb from 900 ft to 8700 ft in WY.