Приводим все дроби к общим знаменателям:
1) 1/2 + 4/7 - 3/14 = (7+8-3) / 14 = 12/14 = 6/7
2) 1/5 - 2/15 + 1/30 = (6-4+1) / 30 = 3/30 = 1/10 = 0,1
3) 1/10 + 7/20 - 2/40 = (4+14-2) / 40 = 16/40 = 2/5 = 0,4
4) 17/20 - 3/10 - 11/60 = (51-18-11) / 60 = 22/60 = 11/30
5) 3/20 + 7/10 + 3/40 = (6+28+3) / 40 = 37/40 = 0,925
6) 9/40 + 3/4 - 19/20 = (9+30-38) / 40 = 1/40 = 0,025