А) 8/18 - 8/27 = 4/9 - 8/27 = (4 × 3 - 8 × 1)/27 = 12/27 - 8/27 = 4/27
б) 7/16 - 5/24 = (7 × 3 - 5 × 2)/48 = 21/48 - 10/48 = 11/48
в) 2/11 - 1/12 = (2 × 12 - 1 × 11)/132 = 24/132 - 11/132 = 13/132
г) 12/13 - 15/26 = (12 × 2 - 15 × 1)/26 = 24/26 - 15/26 = 9/26
д) 9/28 - 11/35 = (9 × 5 - 11 × 4)/140 = 45/140 - 44/140 = 1/140
е) 39/40 - 19/28 = (39 × 7 - 19 × 10)/280 = 273/280 - 190/280 = 83/280