To simplify each expression, we need to find a common denominator for the fractions:

1) 3/7 + 5/14
Common denominator: 14
(3/7)*(2/2) + 5/14
6/14 + 5/14
(6 + 5) / 14
11 / 14

2) 8/9 - 7/12
Common denominator: 36
(8/9)*(4/4) - 7/12
32/36 - 21/36
(32 - 21) / 36
11 / 36

3) 11/50 - 3/25 + 1/20
Common denominator: 100
(11/50)(2/2) - (3/25)(4/4) + 1/20
22/100 - 12/100 + 5/100
(22 - 12 + 5) / 100
15 / 100
3 / 20

Therefore, the simplified expressions are:
1) 11/14
2) 11/36
3) 3/20