Условие:

Вычисли устно. Объясни порядок вычислений.
36 + 25 + 64
15 + 18 + 5 + 2
120 + 45 + 80 + 45
350 + 130 + 70 + 50

36 + 25 + 64 = 125
15 + 18 + 5 + 2 = 30
120 + 45 + 80 + 45 = 290
350 + 130 + 70 + 50 = 600
В выражении, содержащем только сложение, вычисления можно выполнять в любом порядке.
Вычисления:
36 + 25 + 64 = (36 + 64) + 25 = 100 + 25 = 125
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}36\\ 64\end{array}}\\ \begin{array}{r}100\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}100\\ 25\end{array}}\\ \begin{array}{r}125\end{array}\end{array}$
15 + 18 + 5 + 2 = (15 + 5) + (8 + 2) = 20 + 10 = 30
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}15\\ 5\end{array}}\\ \begin{array}{r}20\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}8\\ 2\end{array}}\\ \begin{array}{r}10\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}20\\ 10\end{array}}\\ \begin{array}{r}30\end{array}\end{array}$
120 + 45 + 80 + 45 = (120 + 80) + (45 + 45) = 200 + 90 = 290
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}120\\ 80\end{array}}\\ \begin{array}{r}200\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}45\\ 45\end{array}}\\ \begin{array}{r}90\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}200\\ 90\end{array}}\\ \begin{array}{r}290\end{array}\end{array}$
350 + 130 + 70 + 50 = (350 + 50) + (70 + 130) = 400 + 200 = 600
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}350\\ 50\end{array}}\\ \begin{array}{r}400\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}70\\ 130\end{array}}\\ \begin{array}{r}200\end{array}\end{array}$
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}400\\ 200\end{array}}\\ \begin{array}{r}600\end{array}\end{array}$