1) 1/2 -1/3 -1/4 = -1/12
1/2 = 6/12. 1/3 = 4/12. 1/4 = 3/12
6/12 - 4/12 - 3/12 = -1/12
2) 2/3 - 1/4 - 1/6 = 1/4
2/3 = 8/12. 1/4 = 3/12. 1/6 = 2/12
8/12 - 3/12 - 2/12 = 3/12 = 1/4
3) 1/8 -1/4-1/2 = -5/8
1/8 = 2/16. 1/4 = 4/16. 1/2 = 8/16
2/16 - 4/16 - 8/16 = -10/16 = -5/8