4/8 = 2/8 +2/8 =8/8-4/8
7/9=3/9+4/9=10/9-3/9
5/7=4/7+1/7=6/7-1/7
3/5=2/5+1/5=4/5-1/5
2/6=1/6+1/6=4/6-2/6
3/4=2/4+1/4=4/4-1/4