Many of us are not the best typists and occasionally miss an obvious typo due to eyesight or other problems.
RV's are heavy and have much rolling resistance and are not well streamlined. Aerodynamic drag builds up greatly as speed increases. Expect 7-10 mpg with gasoline engine power, at 55-65mph in average driving conditions, with some head and side winds, some hills and flat lands. Cost of diesel fuel and higher initial cost of diesel powered RV's requires lots of driving to justify the added cost.