Correction :

8 + 7 = 15	4 + 18 = 22
0 + 9 = 9	21 + 16 = 37
6 : 6 = 1	10 + 2 = 12
31 - 17 = 14	44 - 24 = 20
23 + 24 = 47	15 + 5 = 20
15 - 3 = 12	21 : 3 = 7
17 + 3 = 20	12 + 13 = 25
10 - 4 = 6	2 + 15 = 17
10 - 9 = 1	7 + 10 = 17
31 - 7 = 24	8 + 5 = 13