Условие:

Вычисли.
(39 − 17) + 20
59 − (32 + 13)
(67 + 12) − 55
23 + (97 − 86)
(90 − 50) − 10
10 + (20 + 45)

(39 − 17) + 20 = 42
59 − (32 + 13) = 14
(67 + 12) − 55 = 24
23 + (97 − 86) = 34
(90 − 50) − 10 = 30
10 + (20 + 45) = 75
Вычисления:
(39 − 17) + 20 = 22 + 20 = 42
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}39\\ 17\end{array}}\\ \begin{array}{r}22\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}22\\ 20\end{array}}\\ \begin{array}{r}42\end{array}\end{array}$
59 − (32 + 13) = 59 − 45 = 14
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}32\\ 13\end{array}}\\ \begin{array}{r}45\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}59\\ 45\end{array}}\\ \begin{array}{r}14\end{array}\end{array}$
(67 + 12) − 55 = 79 − 55 = 24
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}67\\ 12\end{array}}\\ \begin{array}{r}79\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}79\\ 55\end{array}}\\ \begin{array}{r}24\end{array}\end{array}$
23 + (97 − 86) = 23 + 11 = 34
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}97\\ 86\end{array}}\\ \begin{array}{r}11\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}23\\ 11\end{array}}\\ \begin{array}{r}34\end{array}\end{array}$
(90 − 50) − 10 = 40 − 10 = 30
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}90\\ 50\end{array}}\\ \begin{array}{r}40\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}40\\ 10\end{array}}\\ \begin{array}{r}30\end{array}\end{array}$
10 + (20 + 45) = 10 + 65 = 75
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}20\\ 45\end{array}}\\ \begin{array}{r}65\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}10\\ 65\end{array}}\\ \begin{array}{r}75\end{array}\end{array}$