23 + 7
20 − 5
66 + 4
77 + 8
19 + 6
83 − 9
29 + 0
0 + 0
17 − 17
9 + 9 + 9
8 + 8 + 8 + 8
7 + 7 + 7 + 7 + 7
23 + 7 = 20 + 3 + 7 = 20 + 10 = 30
20 − 5 = (10 + 10) − 5 = 10 + (10 − 5) = 10 + 5 = 15
66 + 4 = 60 + 6 + 4 = 60 + 10 = 70
77 + 8 = 77 + (3 + 5) = (77 + 3) + 5 = 80 + 5 = 85
19 + 6 = 19 + (1 + 5) = (19 + 1) + 5 = 20 + 5 = 25
83 − 9 = 83 − 3 − 6 = 80 − 6 = 70 + (10 − 6) = 70 + 4 = 74
29 + 0 = 29
0 + 0 = 0
17 − 17 = 0
9 + 9 + 9 = 9 + (1 + 1 + 7) + 9 = (9 + 1) + (9 + 1) + 7 = 10 + 10 + 7 = 20 + 7 = 27
8 + 8 + 8 + 8 = 8 + 8 + (2 + 6) + (2 + 6) = (8 + 2) + (8 + 2) + (6 + 6) = 10 + 10 + (6 + 4 + 2) = 20 + (10 + 2) = 20 + 10 + 2 = 30 + 2 = 32
7 + 7 + 7 + 7 + 7 = 7 + (3 + 4) + 7 + (3 + 1 + 3) + 7 = (7 + 3) + (7 + 3) + (7 + 3) + (4 + 1) = 10 + 10 + 10 + 5 = 20 + 10 + 5 = 30 + 5 = 35
