7/9 - 5/7 = 49/63 - 35/63 = 14/63
2/3 + 7/8 = 16/24 + 21/24 = 37/24 = 1 13/24
3/4 - 1/6 = 9/12 - 2/12 = 7/12
5/6 + 1/9 = 15/18 + 2/18 = 17/18
8/25 + 17/20 = 32/100 + 85/100 = 117/100 = 1,17
4/45 - 1/30 = 8/90 - 3/90 = 5/90 = 1/18
17/18 - 11/12 = 34/36 - 33/36 = 1/36
11/15 + 5/12 = 44/60 + 25/60 = 69/60 = 1 9/60 = 1 3/20
1/3 + 1/6 = 2/6 + 1/6 = 3/6 = 1/2
3/4 - 2/5 = 15/20 - 8/20 = 7/20