7,429x + 9,571x = 4,25
17x = 4,25
x = 4,25 : 17
x = 0,25
Ответ: 0,25

Вычисления:
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}\mathrm{7,429}\\ \mathrm{9,571}\end{array}}\\ \begin{array}{r}\mathrm{17,000 }\end{array}\end{array}$
 
$\begin{array}{cc}\begin{array}{l}\underset{¯}{\phantom{0}}\mathrm{4,25}\\ \phantom{0}\underset{¯}{34}\\ \phantom{0}\underset{¯}{\phantom{0}}85\\ \phantom{00}\underset{¯}{85}\\ \phantom{000}0\end{array}& \begin{array}{l}\overline{)17}\\ \overline{\overline{)\mathrm{0,25}}}\end{array}\end{array}$

28x − x = 0,729
27x = 0,729
x = 0,729 : 27
x = 0,027
Ответ: 0,027

Вычисления:
$\begin{array}{cc}\begin{array}{l}\underset{¯}{\phantom{0}}\mathrm{0,729}\\ \phantom{0}\underset{¯}{54}\\ \underset{¯}{\phantom{0}}189\\ \phantom{0}\underset{¯}{189}\\ \phantom{000}0\end{array}& \begin{array}{l}\overline{)27}\\ \overline{\overline{)\mathrm{0,027}}}\end{array}\end{array}$

1,5x − 0,78x = 1,8
0,72x = 1,8
x = 1,8 : 0,72
x = 2,5
Ответ: 2,5

Вычисления:
$\begin{array}{r}\begin{array}{r}-\end{array}\underline{\begin{array}{r}\mathrm{1,50}\\ \mathrm{0,78}\end{array}}\\ \begin{array}{r}\mathrm{0,72 }\end{array}\end{array}$
 
$\begin{array}{cc}\begin{array}{l}\underset{¯}{\phantom{0}}180\\ \phantom{0}\underset{¯}{144}\\ \phantom{0}\underset{¯}{\phantom{0}}360\\ \phantom{00}\underset{¯}{360}\\ \phantom{0000}0\end{array}& \begin{array}{l}\overline{)72}\\ \overline{\overline{)\mathrm{2,5}}}\end{array}\end{array}$

3,6y + 2,8y = 22,4
6,4y = 22,4
y = 22,4 : 6,4
y = 3,5
Ответ: 3,5

Вычисления:
$\begin{array}{r}\begin{array}{r}+\end{array}\underline{\begin{array}{r}\mathrm{3,6}\\ \mathrm{2,8}\end{array}}\\ \begin{array}{r}\mathrm{22,4 }\end{array}\end{array}$
 
$\begin{array}{cc}\begin{array}{l}\underset{¯}{\phantom{0}}224\\ \phantom{0}\underset{¯}{192}\\ \phantom{0}\underset{¯}{\phantom{0}}320\\ \phantom{00}\underset{¯}{320}\\ \phantom{0000}0\end{array}& \begin{array}{l}\overline{)64}\\ \overline{\overline{)\mathrm{3,5}}}\end{array}\end{array}$