Correction :

28 - 10 = 18	3 + 15 = 18
23 - 12 = 11	55 : 11 = 5
17 + 9 = 26	6 - 6 = 0
23 + 9 = 32	24 - 3 = 21
21 + 19 = 40	12 + 15 = 27
11 × 2 = 22	5 + 8 = 13
5 + 3 = 8	9 - 3 = 6
23 - 10 = 13	16 + 15 = 31
8 + 12 = 20	9 : 9 = 1
8 + 10 = 18	30 - 21 = 9