Correction :

20 + 12 = 32	4 - 4 = 0
24 - 5 = 19	20 - 13 = 7
20 + 19 = 39	11 + 20 = 31
3 + 7 = 10	24 - 1 = 23
11 + 10 = 21	16 - 16 = 0
4 + 4 = 8	11 - 4 = 7
44 : 4 = 11	20 - 2 = 18
19 + 17 = 36	5 + 4 = 9
16 + 23 = 39	13 - 3 = 10
3 + 14 = 17	20 - 9 = 11