1)

2 3/4 - 1 5/6 = 2 9/12 - 1 10/12 = 1 21/12 - 1 10/12 = 11/12,

2)

4 2/5 + 3 5/6 = 4 12/30 + 3 25/30 = 7 37/30 = 8 7/30,

3)

7 5/12 - (1 5/8 + 2 1/24) = 7 5/12 - 1 5/8 - 2 1/24 = 7 10/24 - 1 15/24 - 2 1/24 =

= 6 34/24 - 1 15/24 - 2 1/24 = 3 18/24 = 3 3/4