Correction :

19 - 12 = 7	23 + 19 = 42
42 - 23 = 19	26 - 13 = 13
10 + 11 = 21	20 - 16 = 4
32 - 13 = 19	11 + 20 = 31
40 - 16 = 24	21 - 2 = 19
25 - 13 = 12	10 × 2 = 20
4 + 23 = 27	39 - 16 = 23
22 + 18 = 40	26 - 11 = 15
28 - 22 = 6	6 + 20 = 26
18 + 2 = 20	1 × 1 = 1