:1)1/5-1/6; 2)3/4-1/3; 3)7/9-2/11; 4)3/4-4/9; 5)7/8-5/12; 6)11/12-11/18

Чтобы это решить, сделаем НОЗ каждой дроби:

1) 1/5 - 1/6 = (НОЗ: 30) = 1*6/30 - 1*5/30 = 6/30 - 5/30 = 1/30

2) 3/4 - 1/3 = (НОЗ: 12) = 3*3/12 - 1*4/12 = 9/12 - 4/12 = 5/12

3) 7/9 - 2/11 = (НОЗ: 99) = 7*11/99 - 2*9/99 = 77/99 - 18/99 = 59/99

4) 3/4 - 4/9 = (НОЗ: 36) = 3*9/36 - 4*4/36 = 27/36 - 16/36 = 9/36 = 1/4

5) 7/8 - 5/12 = (НОЗ: 24) = 7*3/24 - 5*2/24 = 21/24 - 10/24 = 11/24

6) 11/12 - 11/18 = (НОЗ: 36) = 11*3/36 - 11*2/36 = 33/36 - 22/36 = 11/36