Correction :

26 - 17 = 9	24 - 22 = 2
13 - 11 = 2	31 - 12 = 19
15 + 12 = 27	27 - 12 = 15
14 : 7 = 2	2 + 21 = 23
19 + 23 = 42	19 + 0 = 19
8 : 1 = 8	15 + 7 = 22
44 - 24 = 20	80 : 10 = 8
21 + 7 = 28	8 × 4 = 32
17 + 19 = 36	17 + 20 = 37
17 - 13 = 4	13 + 2 = 15