Correction :

6 × 7 = 42	32 - 24 = 8
24 + 11 = 35	23 - 23 = 0
40 - 18 = 22	5 + 4 = 9
20 - 19 = 1	9 + 17 = 26
34 - 15 = 19	11 + 13 = 24
2 + 20 = 22	15 - 5 = 10
19 - 7 = 12	5 : 1 = 5
16 + 9 = 25	8 : 2 = 4
41 - 23 = 18	15 + 17 = 32
17 + 21 = 38	31 - 15 = 16