Correction :

15 + 20 = 35	30 - 19 = 11
13 + 3 = 16	24 - 20 = 4
7 - 4 = 3	21 + 13 = 34
29 - 10 = 19	2 + 17 = 19
22 - 9 = 13	22 + 18 = 40
13 + 23 = 36	43 - 24 = 19
14 + 8 = 22	4 : 4 = 1
25 - 6 = 19	7 + 9 = 16
3 × 9 = 27	8 × 6 = 48
10 - 1 = 9	19 + 21 = 40