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1. \(27 + 10 = \ldots\)
2. \(55 + 22 = \ldots\)
3. \(87 + 10 = \ldots\)
4. \(57 + 40 = \ldots\)
5. \(15 + 80 = \ldots\)
6. \(76 + 22 = \ldots\)
7. \(48 + 30 = \ldots\)
8. \(66 + 22 = \ldots\)
9. \(25 + 61 = \ldots\)
10. \(17 + 12 = \ldots\)
11. \(70 + 21 = \ldots\)
12. \(69 + 20 = \ldots\)

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Verbetersleutel

1. \(\begin{align} & 27 + 10\\= &10+27\\= &10 + \color{green}{20} + \color{red}{7} \\= & \color{green}{30} + \color{red}{7} \\= & \color{red}{37} \end{align}\)
2. \(\begin{align} & 55 + 22\\= & \color{green}{50} + \color{red}{5} + \color{green}{20} + \color{red}{2} \\= & \color{green}{70} + \color{red}{7} \\= & \color{red}{77} \end{align}\)
3. \(\begin{align} & 87 + 10\\= &10+87\\= &10 + \color{green}{80} + \color{red}{7} \\= & \color{green}{90} + \color{red}{7} \\= & \color{red}{97} \end{align}\)
4. \(\begin{align} & 57 + 40\\= &40+57\\= &40 + \color{green}{50} + \color{red}{7} \\= & \color{green}{90} + \color{red}{7} \\= & \color{red}{97} \end{align}\)
5. \(\begin{align} & 15 + 80\\= &80+15\\= &80 + \color{green}{10} + \color{red}{5} \\= & \color{green}{90} + \color{red}{5} \\= & \color{red}{95} \end{align}\)
6. \(\begin{align} & 76 + 22\\= & \color{green}{70} + \color{red}{6} + \color{green}{20} + \color{red}{2} \\= & \color{green}{90} + \color{red}{8} \\= & \color{red}{98} \end{align}\)
7. \(\begin{align} & 48 + 30\\= &30+48\\= &30 + \color{green}{40} + \color{red}{8} \\= & \color{green}{70} + \color{red}{8} \\= & \color{red}{78} \end{align}\)
8. \(\begin{align} & 66 + 22\\= & \color{green}{60} + \color{red}{6} + \color{green}{20} + \color{red}{2} \\= & \color{green}{80} + \color{red}{8} \\= & \color{red}{88} \end{align}\)
9. \(\begin{align} & 25 + 61\\= & \color{green}{20} + \color{red}{5} + \color{green}{60} + \color{red}{1} \\= & \color{green}{80} + \color{red}{6} \\= & \color{red}{86} \end{align}\)
10. \(\begin{align} & 17 + 12\\= & \color{green}{10} + \color{red}{7} + \color{green}{10} + \color{red}{2} \\= & \color{green}{20} + \color{red}{9} \\= & \color{red}{29} \end{align}\)
11. \(\begin{align} & 70 + 21\\= &70 + \color{green}{20} + \color{red}{1} \\= & \color{green}{90} + \color{red}{1} \\= & \color{red}{91} \end{align}\)
12. \(\begin{align} & 69 + 20\\= &20+69\\= &20 + \color{green}{60} + \color{red}{9} \\= & \color{green}{80} + \color{red}{9} \\= & \color{red}{89} \end{align}\)