Calculate: 10.01+9.9

Expression: $10.01+9.9$

Add the digits of the bolded column $1+0=1$

$\frac{\begin{matrix}\:\:&1&0&.&0&\bold{1}\\+&0&9&.&9&\bold{0}\end{matrix}}{\begin{matrix}\:\:&\:\:&\:\:&\:\:&\:\:&\bold{1}\end{matrix}}$

Add the digits of the bolded column $0+9=9$

$\frac{\begin{matrix}\:\:&1&0&.&\bold{0}&1\\+&0&9&.&\bold{9}&0\end{matrix}}{\begin{matrix}\:\:&\:\:&\:\:&\:\:&\bold{9}&1\end{matrix}}$

Place the decimal point in the answer directly below the decimal points in the terms

$\frac{\begin{matrix}\:\:&1&0&\bold{.}&0&1\\+&0&9&\bold{.}&9&0\end{matrix}}{\begin{matrix}\:\:&\:\:&\:\:&\bold{.}&9&1\end{matrix}}$

Add the digits of the bolded column $0+9=9$

$\frac{\begin{matrix}\:\:&1&\bold{0}&.&0&1\\+&0&\bold{9}&.&9&0\end{matrix}}{\begin{matrix}\:\:&\:\:&\bold{9}&.&9&1\end{matrix}}$

Add the digits of the bolded column $1+0=1$

$\frac{\begin{matrix}\:\:&\bold{1}&0&.&0&1\\+&\bold{0}&9&.&9&0\end{matrix}}{\begin{matrix}\:\:&\bold{1}&9&.&9&1\end{matrix}}$

Write the numbers one under the other, line up the decimal points. $
$Add trailing zeroes so the numbers have the same length.

$\begin{matrix}\:\:&1&0&.&0&1\\+&0&9&.&9&0\end{matrix}$ $=19.91$