Fill in the blanks with the correct number.
1. 2 + 8 = 8 + ___
2. 5 + 4 = 1 + ___
3. 8 + 4 = 1 + ___
4. 7 + 2 = 3 + ___
5. 9 + ___ = 10 + 1
6. 1 + ___ = 5 + 5
7. ___ + 8 = 6 + 6
8. ___ + 4 = 7 + 7
9. 1 + 7 = ___ + 8
10. 7 + 7 = 9 + ___
11. 20 + 4 = 21 + ___
12. 6 + 4 = 2 + ___
13. 7 + 10 = 10 + ___
14. 11 + 1 = 6 + ___
15. 10 + ___ = 6 + 6
16. 19 + ___ = 20 + 0