Hint



4 + 4 =
7 + 7 =
6 + 6 =
I must add: 6 + 5 =
Write the double:
+ + 1
Add the double:
+ 1
Answer =
I must add: 9 + 8 =
Write the double:
+ - 1
Add the double:
- 1
Answer =
I must add: 5 + 4 =
Write the double:
+ - 1
Add the double:
- 1
Answer =
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