Correction :

27 - 17 = 10	8 + 21 = 29
4 × 7 = 28	20 - 0 = 20
11 + 6 = 17	16 + 19 = 35
13 + 5 = 18	40 - 17 = 23
14 + 21 = 35	5 + 21 = 26
14 + 5 = 19	3 - 0 = 3
17 + 4 = 21	4 × 3 = 12
31 - 22 = 9	33 - 24 = 9
11 + 12 = 23	15 + 22 = 37
10 + 2 = 12	11 + 2 = 13