А) 5 5/9 + 2 1/18 = (5 + 2) + (5/9 + 1/18) = 7 + (10/18 + 1/18) = 7 + 11/18 = 7 11/18,
б) 5 7/24 - 3 11/36 = (5 - 3) + (7/24 - 11/36) = 2 + (21/72 - 22/72) = 2 - 1/72 = 144/72 - 1/72 = 143/72 = 1 71/72,
в) 2 9/26 + 3 7/39 - 4 7/13 = (2 + 3 - 4) + (9/26 + 7/39 - 7/13) = 1 + (27/78 + 14/78 - 42/78) = 1 - 41/78 = 78/78 - 41/78 = 37/78