Условие:

Вычисли устно.
30 + 40
30 − 10
90 + 10
90 − 10
60 + 5
75 − 5
88 − 8
96 − 6
(40 + 40) − 30
(80 − 30) + 20
(20 + 30) − 10
(90 − 50) − 30

30 + 40 = 70
30 − 10 = 20
90 + 10 = 100
90 − 10 = 80
60 + 5 = 65
75 − 5 = 70
88 − 8 = 80
96 − 6 = 90
(40 + 40) − 30 = 50
(80 − 30) + 20 = 70
(20 + 30) − 10 = 40
(90 − 50) − 30 = 10
Вычисления:
30 + 10 = 40
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}30\\ 10\end{array}}\\ \begin{array}{r}40\end{array}\end{array}$
30 − 10 = 20
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}30\\ 10\end{array}}\\ \begin{array}{r}20\end{array}\end{array}$
90 + 10 = 100
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}90\\ 10\end{array}}\\ \begin{array}{r}100\end{array}\end{array}$
90 − 10 = 80
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}90\\ 10\end{array}}\\ \begin{array}{r}80\end{array}\end{array}$
60 + 5 = 65
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}60\\ 5\end{array}}\\ \begin{array}{r}65\end{array}\end{array}$
75 − 5 = 70
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}75\\ 5\end{array}}\\ \begin{array}{r}70\end{array}\end{array}$
88 − 8 = 80
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}88\\ 8\end{array}}\\ \begin{array}{r}80\end{array}\end{array}$
96 − 6 = 90
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}96\\ 6\end{array}}\\ \begin{array}{r}90\end{array}\end{array}$
(40 + 40) − 30 = 80 − 30 = 50
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}40\\ 40\end{array}}\\ \begin{array}{r}80\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}80\\ 30\end{array}}\\ \begin{array}{r}50\end{array}\end{array}$
(80 − 30) + 20 = 50 + 20 = 70
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}80\\ 30\end{array}}\\ \begin{array}{r}50\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}50\\ 20\end{array}}\\ \begin{array}{r}70\end{array}\end{array}$
(20 + 30) − 10 = 50 − 10 = 40
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}20\\ 30\end{array}}\\ \begin{array}{r}50\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}50\\ 10\end{array}}\\ \begin{array}{r}40\end{array}\end{array}$
(90 − 50) − 30 = 40 − 30 = 10
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}90\\ 50\end{array}}\\ \begin{array}{r}40\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}40\\ 30\end{array}}\\ \begin{array}{r}10\end{array}\end{array}$