12 5/12 + 4 1/8 - 4 2/3 = (12 + 4 - 4) + (10/24 + 3/24 - 16/24) = 12 + (- 3/24) = 11 + (24/24 - 3/24) = 11 + 21/24 = 11 21/24 = 11 7/8
5 9/10 + (5 - 2 8/15) = 5 9/10 + (4 15/15 - 2 8/15) = 5 9/10 + 2 7/15 = (5 + 2) + ( 27/30 + 14/30) = 7 + 41/30 = 8 11/30
