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1. \(8 + \color{red}{9} = \)
2. \(9 + \color{red}{2} = \)
3. \(7 + \color{red}{6} = \)
4. \(4 + \color{red}{10} = \)
5. \(9 + \color{red}{9} = \)
6. \(6 + \color{red}{10} = \)
7. \(5 + \color{red}{7} = \)
8. \(7 + \color{red}{13} = \)
9. \(5 + \color{red}{9} = \)
10. \(6 + \color{red}{12} = \)
11. \(2 + \color{red}{18} = \)
12. \(7 + \color{red}{11} = \)

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Verbetersleutel

1. \(8 + \color{red}{9} = 9 + \color{green}{8} = 9 + \color{green}{1 + 7} = 17\)
2. \(9 + \color{red}{2} = 9 + \color{red}{1} \color{red}{ + } \color{red}{1} = 11\)
3. \(7 + \color{red}{6} = 7 + \color{red}{3} \color{red}{ + } \color{red}{3} = 13\)
4. \(4 + \color{red}{10} = \color{red}{10} + 4 = 14\)
5. \(9 + \color{red}{9} = 9 + \color{red}{1} \color{red}{ + } \color{red}{8} = 18\)
6. \(6 + \color{red}{10} = \color{red}{10} + 6 = 16\)
7. \(5 + \color{red}{7} = 7 + \color{green}{5} = 7 + \color{green}{3 + 2} = 12\)
8. \(7 + \color{red}{13} = \color{red}{13} + 7 = 20\)
9. \(5 + \color{red}{9} = 9 + \color{green}{5} = 9 + \color{green}{1 + 4} = 14\)
10. \(6 + \color{red}{12} = \color{red}{12} + 6 = 18\)
11. \(2 + \color{red}{18} = \color{red}{18} + 2 = 20\)
12. \(7 + \color{red}{11} = \color{red}{11} + 7 = 18\)