1/2 + 2/3 = 3/6+4/6 = 7/6 .
3/4+1/6 = 9/12+2/12 = 11/12
1/20-1/30 = 3/60-2/60 = 1/60
5/12-7/18 = 15/36 - 14/36 = 1/36
1/50+1/75 = 3/150+2/150 = 5/150 = 1/30
1/2+1/3+5/6 = 3/6+2/6+5/6 = 10/6
4/3+1/4-5/6 = 16/12+3/12-10/12 = 8/12 = 2/3
1/2-1/5 +7/10 = 5/10-2/10+ 7/10 = 10/10 = 1 .
