CHALLENGE 12: Adding 9 and 11 to double digit numbers
Strategies:
1. To add 9, add 10 and then subtract 1.
2. To add 11, add 10 and then add 1 more.
27 + 9 =
40 + 11 =
58 + 9 =
18 + 11 =
35 + 11 =
89 + 11 =
27 + 9 =
63 + 9 =
26 + 11 =
85 + 9 =
66 + 9 =
73 + 11 =
27 + 11 =
57 + 11 =
67 + 9 =
16 + 9 =
22 + 11 =
63 + 11 =
32 + 9 =
67 + 11 =
55 + 9 =
28 + 11 =
65 + 9 =
67 + 11 =
17 + 11 =
38 + 9 =
26 + 9 =
34 + 9 =
85 + 9 =
53 + 9 =
30 + 11 =
25 + 11 =
45 + 11 =
83 + 9 =
18 + 11 =
35 + 9 =
63 + 9 =
37 + 11 =
71 + 9 =
52 + 11 =
65 + 9 =
29 + 11 =
75 + 9 =
26 + 9 =
64 + 11 =
54 + 11 =
67 + 11 =
56 + 11 =