To find the sum of each pair of fractions, we need to first find a common denominator and then add or subtract the fractions accordingly.

1/12 + 1/6
Common denominator: 12
(1/12) + (2/12) = 3/12 = 1/4

3/4 + 1/6
Common denominator: 12
(9/12) + (2/12) = 11/12

1/2 + 3/5
Common denominator: 10
(5/10) + (6/10) = 11/10 = 1 1/10

2/11 + 1/3
Common denominator: 33
(6/33) + (11/33) = 17/33

2/3 - 3/4
Common denominator: 12
(8/12) - (9/12) = -1/12

1/4 + 4/5
Common denominator: 20
(5/20) + (16/20) = 21/20 = 1 1/20

1/2 + 1/4 - 1/8
Common denominator: 8
(4/8) + (2/8) - (1/8) = 5/8

Therefore,

1/12 + 1/6 = 1/43/4 + 1/6 = 11/121/2 + 3/5 = 1 1/102/11 + 1/3 = 17/332/3 - 3/4 = -1/121/4 + 4/5 = 1 1/201/2 + 1/4 - 1/8 = 5/8.