Basis Optellen

Reken uit

\(2 + 9 = \)

\(\begin{align} & 2 + 9 \\= & 9 + 2 \\= & 9 + \color{green}{1} + \color{red}{1} \\= & \color{green}{10} + \color{red}{1} \\= & \color{red}{11} \end{align}\)