20 + 25 = 45
40 + 25 = 65
15 + 25 = 40
38 + 25 = 63

30 + 20 = 50
30 + 40 = 70
30 + 15 = 45
30 + 38 = 68

20 − 15 = 5
40 − 15 = 25
15 − 15 = 0
38 − 15 = 23

80 − 20 = 60
80 − 40 = 40
80 − 15 = 65
80 − 38 = 42
Вычисления:
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}20\\ 25\end{array}}\\ \begin{array}{r}45\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}40\\ 25\end{array}}\\ \begin{array}{r}65\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}15\\ 25\end{array}}\\ \begin{array}{r}40\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}38\\ 25\end{array}}\\ \begin{array}{r}63\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}30\\ 20\end{array}}\\ \begin{array}{r}50\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}30\\ 40\end{array}}\\ \begin{array}{r}70\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}30\\ 15\end{array}}\\ \begin{array}{r}45\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}30\\ 38\end{array}}\\ \begin{array}{r}68\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}20\\ 15\end{array}}\\ \begin{array}{r}5\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}40\\ 15\end{array}}\\ \begin{array}{r}25\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}15\\ 15\end{array}}\\ \begin{array}{r}0\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}38\\ 15\end{array}}\\ \begin{array}{r}23\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}80\\ 20\end{array}}\\ \begin{array}{r}60\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}80\\ 40\end{array}}\\ \begin{array}{r}40\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}80\\ 15\end{array}}\\ \begin{array}{r}65\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}80\\ 38\end{array}}\\ \begin{array}{r}42\end{array}\end{array}$