Пошаговое объяснение:

№1

1/2 - 1/6 = 3/6 - 1/6 = 2/6 = 1/3

11/15 - 3/5 = 11/15 - 9/15 = 2/15

4/5 - 13/20 = 16/20 - 13/20 = 3/20

5/6 - 13/18 = 15/18 - 13/18 = 2/18 = 1/9