Correction :

10 + 2 = 12	2 × 2 = 4
23 - 21 = 2	20 - 9 = 11
32 : 4 = 8	28 - 7 = 21
22 + 17 = 39	33 - 24 = 9
13 + 5 = 18	20 + 5 = 25
32 - 17 = 15	17 - 2 = 15
18 + 15 = 33	23 - 22 = 1
0 + 4 = 4	30 - 9 = 21
20 - 10 = 10	13 - 8 = 5
8 - 1 = 7	10 + 20 = 30