Correction :

47 - 23 = 24	28 - 12 = 16
42 - 18 = 24	5 - 2 = 3
24 - 2 = 22	24 - 24 = 0
5 + 18 = 23	8 + 5 = 13
11 × 9 = 99	9 × 6 = 54
6 + 19 = 25	27 - 5 = 22
64 : 8 = 8	7 + 8 = 15
20 - 2 = 18	3 + 5 = 8
29 - 6 = 23	34 - 21 = 13
4 + 12 = 16	15 + 16 = 31