13/18 + 7/12 = 26/36 + 21/36 = 47/36 = 1 целая 11/36
5/7 - 3/5 = 25/35 - 21/35 = 4/35
5/6 - 3/8 - 1/12 = 20/24 - 9/24 - 2/24 = 9/24 = 3/8 - сократили на 3.
13/18 + 7/12 = 26/36 + 21/36 = 47/36 = 1 целая 11/36
5/7 - 3/5 = 25/35 - 21/35 = 4/35
5/6 - 3/8 - 1/12 = 20/24 - 9/24 - 2/24 = 9/24 = 3/8 - сократили на 3.