Basis Optellen

Reken uit

\(66 + 19 = \ldots\)

\(\begin{align} & 66 + 19\\= & \color{green}{60} + \color{red}{6} + \color{green}{10} + \color{red}{9} \\= & \color{green}{70} + \color{red}{15} \\= & \color{green}{70} + \color{orange}{10} + \color{red}{5} \\= & \color{orange}{80} + \color{red}{5} \\= & \color{red}{85} \end{align}\)