Correction :

31 - 23 = 8	18 - 16 = 2
29 - 6 = 23	0 + 21 = 21
3 + 22 = 25	54 : 9 = 6
34 - 22 = 12	2 - 1 = 1
42 - 23 = 19	3 × 9 = 27
12 - 12 = 0	13 - 13 = 0
24 - 13 = 11	22 + 1 = 23
26 - 12 = 14	13 + 5 = 18
20 - 8 = 12	13 - 10 = 3
35 : 7 = 5	11 : 11 = 1