Correction :

21 - 20 = 1	19 - 19 = 0
14 + 5 = 19	10 + 23 = 33
16 - 1 = 15	8 - 6 = 2
19 + 18 = 37	36 - 17 = 19
10 + 22 = 32	32 - 15 = 17
22 - 14 = 8	17 + 19 = 36
14 + 7 = 21	13 + 16 = 29
22 - 8 = 14	99 : 11 = 9
8 + 20 = 28	12 : 4 = 3
8 × 2 = 16	9 - 2 = 7