adding 10s
10 + 10 =
20
9
20 + 4 =
24
2 - 1
1
10 + 11 =
21
20 + 10 =
30
5 + 5 + 3
13
30 + 3
33
4 - 2 =
2
30 + 12
42
40 + 20 =
60
6 + 6 + 2
14
30 + 6 =
36
6 - 1 =
5
51 + 23
74
30 + 50 =
80
10 + 2 + 4
16
51 + 9 =
8 - 2
6
56 + 22
78
80 + 20 =
100
15 + 2 + 3
20
22 + 7
29
12 - 6 =
6
46 + 26
72