Просто по действиям.
1)0,9 - 1/3 + 0,75 - 1/15 = 9/10 - 1/3 + 75/100 - 1/15 = 27/30 - 10/30 +3/4 - 1/15 = 17/30 + 3/4 - 1/15 = 34/60 + 45/60 - 4/60 = 75/60 = 1,25
2) 0,5 - 1/6 = 5/10 - 1/6 = 1/2 - 1/6 = 3/6 - 1/6 = 2/6 = 1/3
3) 75/60 : 1/3 = 75/60 x 3/1 = 75/20 = 3,75
4)75/20 : 5/12 = 75/20 x 12/5 = 9
5)5/7 - 0,4 + 11/14 = 5/7 - 4/10 + 11/14 = 5/7 - 2/5 + 11/14 = 25/35 - 14/35 +11/14 = 11/35 + 11/14 = 44/140 + 110/140 = 154/140 = 1,1
6) 2/3 + 0,8 - 7/15 = 2/3 + 8/10 - 7/15 = 2/3 + 4/5 - 7/15 = 10/15 + 12/15 - 7/15 = 1
7)1,1 : 1 = 1,1
8) 1,1 : 11/5 = 11/10 x 5/11 = 1/2 = 0,5