a) 7/10 + 1/10 = 8/10 = 4/5
б) 7/12 + 1/4 = 7/12 + 3/12 = 10/12 = 5/6
в) 1/5 + 2/15 = 3/15 + 2/15 = 5/15 = 1/3
г) 5/6 + 1/9 = 15/18 + 2/18 = 17/18