MEXICO CITY, Oct 20 (Reuters) - Mexican conglomerate Alfa on Wednesday reported a net profit of 2.49 billion pesos ($120.7 million) for the third quarter, versus a net profit of 3.77 billion pesos a year earlier. Monterrey-based Alfa reported total sales of 79.55 billion pesos, versus sales of 67.57 billion from the same period last year. $1= 20.642 pesos at end-September Reporting by Noe Torres Editing by Chris Reese Our Standards: The Thomson Reuters Trust Principles.