Correction :

4 - 2 = 2	8 + 23 = 31
16 + 5 = 21	40 - 19 = 21
22 + 19 = 41	28 - 7 = 21
5 - 1 = 4	72 : 9 = 8
12 + 21 = 33	30 - 18 = 12
8 + 23 = 31	10 + 9 = 19
2 + 18 = 20	18 + 23 = 41
14 + 12 = 26	20 - 10 = 10
44 : 11 = 4	10 + 17 = 27
12 + 8 = 20	13 - 11 = 2