Correction :

1 + 4 = 5	38 - 21 = 17
24 - 12 = 12	22 - 8 = 14
15 + 15 = 30	10 × 4 = 40
15 + 0 = 15	24 - 23 = 1
35 - 23 = 12	6 + 8 = 14
21 + 7 = 28	20 - 17 = 3
2 + 1 = 3	10 - 7 = 3
23 - 7 = 16	21 - 1 = 20
11 + 24 = 35	29 - 23 = 6
2 + 16 = 18	17 + 18 = 35