Correction :

13 + 4 = 17	70 : 7 = 10
25 - 10 = 15	21 - 17 = 4
77 : 7 = 11	8 + 9 = 17
9 × 5 = 45	4 - 4 = 0
22 + 9 = 31	7 + 13 = 20
40 : 5 = 8	28 - 7 = 21
8 × 9 = 72	30 - 23 = 7
10 × 9 = 90	20 + 6 = 26
17 - 5 = 12	20 - 16 = 4
32 - 20 = 12	44 - 20 = 24