вычислите:а)11/40-17/30;б)-9/21+15/14;в)17/20+19/50

а) 33/120-68/120= - 35/120 = -7/25б) 15/14 - 3/7 =15/14 - 6/14 = 9/14в)  85/100+ 38/100 = 123/100 = 1 целая 23/100