Correction :

24 + 4 = 28	5 + 21 = 26
17 + 23 = 40	29 - 17 = 12
15 + 3 = 18	31 - 24 = 7
2 + 13 = 15	0 + 14 = 14
15 + 17 = 32	14 + 22 = 36
24 - 4 = 20	6 : 3 = 2
11 + 9 = 20	26 - 6 = 20
4 + 9 = 13	32 - 13 = 19
44 - 21 = 23	13 - 7 = 6
16 - 13 = 3	1 + 3 = 4