Correction :

31 - 21 = 10	8 - 5 = 3
40 : 5 = 8	39 - 20 = 19
25 - 18 = 7	6 + 1 = 7
9 + 9 = 18	5 + 1 = 6
31 - 23 = 8	28 - 22 = 6
10 + 20 = 30	27 - 6 = 21
3 × 2 = 6	22 + 6 = 28
25 - 7 = 18	8 × 8 = 64
10 - 3 = 7	21 + 16 = 37
14 + 18 = 32	18 - 8 = 10