49/60 + 11/60 - 1/6 = 49/60 + 11/60 - 10/60 = (49+11-10)/60=50/60=5/6

или

49/60 + 11/60 - 1/6 = (49+11)/60 - 1/6 = 60/60 - 1/6 = 1 - 1/6 = 5/6