Correction :

20 + 19 = 39	25 - 8 = 17
28 - 5 = 23	15 - 8 = 7
1 - 1 = 0	0 + 18 = 18
6 : 1 = 6	29 - 19 = 10
11 + 22 = 33	10 × 7 = 70
13 - 7 = 6	12 + 19 = 31
7 + 9 = 16	15 - 7 = 8
21 + 24 = 45	19 - 13 = 6
18 - 2 = 16	44 - 23 = 21
13 + 17 = 30	1 + 3 = 4