Correction :

17 + 10 = 27	11 + 13 = 24
6 + 21 = 27	14 + 7 = 21
19 - 8 = 11	4 + 18 = 22
33 - 15 = 18	12 + 6 = 18
15 - 13 = 2	22 - 22 = 0
27 - 14 = 13	28 : 4 = 7
20 - 11 = 9	25 - 13 = 12
2 + 7 = 9	31 - 20 = 11
11 × 10 = 110	26 - 22 = 4
4 + 23 = 27	3 - 0 = 3