Exercises: addition of natural numbers

Add the following numbers by written addition.

$66 + 91$

For this task you need the following basic knowledge: Written method of addition
$\begin{array}{l} 6 6 \\ +_{1} 9 1 \\ 1 5 7 \end{array}$
$42 + 78$

For this task you need the following basic knowledge: Written method of addition
$\begin{array}{l} 4 2 \\ +_{1} 7_{1} 8 \\ 1 2 0 \end{array}$
$63 + 80$

For this task you need the following basic knowledge: Written method of addition
$\begin{array}{l} 6 3 \\ +_{1} 8 0 \\ 1 4 3 \end{array}$

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