Ricka,
Ethanol contains aprox. 76,000 BTU/Gal and gasoline contains aprox. 115,500 BTU/Gal. E10 (10% ethanol) contains 111,550 BTU/Gal. or roughly 97% of the energy content of gasoline. Depending on the engine, computer, terrain and driving habits you can get somewhat close to your mileage...