Ответ:
13 + 12 = 25 − верно
16 + 4 = 20 − верно
25 + 25 = 60 − неверно, верно будет: 25 + 25 = 50
41 + 9 = 50 − верно
30 + 30 = 60 − верно
8 + 40 = 48 − верно
100 − 50 = 50 − верно
90 − 2 = 78 − неверно, верно будет: 90 − 2 = 88
Вычисления:
13 + 12 = 25
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}13\\ 12\end{array}}\\ \begin{array}{r}25\end{array}\end{array}$
16 + 4 = 20
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}16\\ 4\end{array}}\\ \begin{array}{r}20\end{array}\end{array}$
25 + 25 = 60
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}25\\ 25\end{array}}\\ \begin{array}{r}50\end{array}\end{array}$
41 + 9 = 50
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}41\\ 9\end{array}}\\ \begin{array}{r}50\end{array}\end{array}$
30 + 30 = 60
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}30\\ 30\end{array}}\\ \begin{array}{r}60\end{array}\end{array}$
8 + 40 = 48
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}8\\ 40\end{array}}\\ \begin{array}{r}48\end{array}\end{array}$
100 − 50 = 50
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}100\\ 50\end{array}}\\ \begin{array}{r}50\end{array}\end{array}$
90 - 2 = 78
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}90\\ 2\end{array}}\\ \begin{array}{r}88\end{array}\end{array}$