a) 1/3 = 2/6 = 3/9
б) 1/4 = 2/8 = 3/12 = 4/16 = 5/20 = 6/24 = 7/28
в) 2/5 = 4/10 = 6/15 = 8/20 = 10/25 = 12/30 = 14/35