Пошаговое объяснение:

28/35 = (28:7)/(35:7) = 4/5

250/1000 = (250:250)/(1000:250) = 1/4

55/4000 = (55:5)/(4000:5) = 11/800

15/3 = 15 : 3 = 5

39/91 = (39:13)/(91:13) = 3/7

60/144 = (60:12)/(144:12) = 5/12