OPetroW 4/5+2/3 = 12/15 + 10/15 = 22/15 = 1 7/15
5/6+7/9 = 15/18 + 14/18 = 29/18 = 1 11/18
3/4-1/6 = 9/12 - 2/12 = 7/12
7/8-5/8 = 2/8 = 1/4
4/9+6/27 = 12/27 + 6/27 = 18/27 = 2/3
9/10+4/5 = 9/10 + 8/10 = 17/10 = 1 7/10
5/6-2/3 = 5/6 - 4/6 = 1/6
5/7-9/14 = 10/14 - 9/14 = 1/14