Решебник по математике 6 класс Виленкин Часть 1, 2 Часть 2. Параграф 4. Действия с рациональными числами Задание 143

\[\boxed{\mathbf{4.}\mathbf{143}}\]

\[\textbf{а)}\ \frac{2}{3}x + \frac{4}{9}x = 3,2\]

\[\frac{6}{9}x + \frac{4}{9}x = 3,2\]

\[\frac{10}{9}x = 3,2\]

\[10x = 3,2 \cdot 9\]

\[10x = 28,8\]

\[x = 2,88.\]

\[\textbf{б)}\ \frac{5}{12}x - \frac{4}{15}x = 0,51\]

\[\frac{25}{60}x - \frac{16}{60}x = 0,51\]

\[\frac{9}{60}x = 0,51\]

\[\frac{3}{20}x = 0,51\]

\[3x = 0,51 \cdot 20\]

\[x = 10,2\ :3\]

\[x = 3,4.\]

\[\textbf{в)}\ x - 0,2x = \frac{8}{15}\]

\[0,8x = \frac{8}{15}\]

\[x = \frac{8}{15}\ :0,8 = \frac{8}{15} \cdot \frac{1}{0,8} = \frac{10}{15}\]

\[x = \frac{2}{3}.\]

\[\textbf{г)}\ x + 1,4x = \frac{6}{25}\]

\[2,4x = \frac{6}{25}\]

\[x = \frac{6}{25}\ :2,4 = \frac{6}{25} \cdot \frac{1}{2,4} =\]

\[= \frac{1}{25 \cdot 0,4} = \frac{1}{10}\]

\[x = 0,1.\ \]