0,8 + 0,2 = 1
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}\mathrm{0,8}\\ \mathrm{0,2}\end{array}}\\ \begin{array}{r}\mathrm{1,0 }\end{array}\end{array}$

0,88 + 0,02 = 0,9
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}\mathrm{0,88}\\ \mathrm{0,02}\end{array}}\\ \begin{array}{r}\mathrm{0,90 }\end{array}\end{array}$

0,888 + 0,002 = 0,89
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}\mathrm{0,888}\\ \mathrm{0,002}\end{array}}\\ \begin{array}{r}\mathrm{0,890 }\end{array}\end{array}$

0,8888 + 0,0002 = 0,889
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}\mathrm{0,8888}\\ \mathrm{0,0002}\end{array}}\\ \begin{array}{r}\mathrm{0,8890 }\end{array}\end{array}$

0,88 + 0,2 = 1,08
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}\mathrm{0,88}\\ \mathrm{0,20}\end{array}}\\ \begin{array}{r}\mathrm{1,08 }\end{array}\end{array}$

0,888 + 0,02 = 0,908
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}\mathrm{0,888}\\ \mathrm{0,020}\end{array}}\\ \begin{array}{r}\mathrm{0,908 }\end{array}\end{array}$

0,88 + 0,12 = 1
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}\mathrm{0,88}\\ \mathrm{0,12}\end{array}}\\ \begin{array}{r}\mathrm{1,00 }\end{array}\end{array}$

0,888 + 0,012 = 0,9
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}\mathrm{0,888}\\ \mathrm{0,012}\end{array}}\\ \begin{array}{r}\mathrm{0,900 }\end{array}\end{array}$