Условие:

Вычисли устно.
40 + 30
60 + 20
70 + 3
80 − 1
60 − 10
90 − 80
78 − 8
55 − 50
60 + 4
90 − 20
68 − 60
99 + 1

40 + 30 = 70
60 + 20 = 80
70 + 3 = 73
80 − 1 = 79
60 − 10 = 50
90 − 80 = 10
78 − 8 = 70
55 − 50 = 5
60 + 4 = 64
90 − 20 = 70
68 − 60 = 8
99 + 1 = 100
Вычисления:
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}40\\ 30\end{array}}\\ \begin{array}{r}70\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}60\\ 20\end{array}}\\ \begin{array}{r}80\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}60\\ 10\end{array}}\\ \begin{array}{r}50\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}90\\ 80\end{array}}\\ \begin{array}{r}10\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}90\\ 20\end{array}}\\ \begin{array}{r}70\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}68\\ 60\end{array}}\\ \begin{array}{r}8\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}55\\ 50\end{array}}\\ \begin{array}{r}5\end{array}\end{array}$