Brug Mix (reeks 1)

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\(28 + 11 = \ldots\)

\(\begin{align} & 28 + 11\\= & \color{green}{20} + \color{red}{8} + \color{green}{10} + \color{red}{1} \\= & \color{green}{30} + \color{red}{9} \\= & \color{red}{39} \end{align}\)