Correction :

15 + 5 = 20	9 + 13 = 22
4 + 11 = 15	26 - 2 = 24
2 × 4 = 8	24 - 23 = 1
11 + 0 = 11	25 - 20 = 5
19 + 21 = 40	35 - 13 = 22
7 + 20 = 27	9 - 1 = 8
36 - 12 = 24	43 - 20 = 23
16 - 12 = 4	23 + 2 = 25
6 × 3 = 18	12 + 14 = 26
44 - 21 = 23	30 - 13 = 17