10) 13 5/9 - 3 8/9 = (13 - 3) + (5/9 - 8/9) = 10 - 3/9 = 9 2/9

12) 23 7/8 - 5 5/8 = (23 - 5) + (7/8 - 5/8) = 18 + 2/8 = 18 1/4