Đáp án: $x=\dfrac{29}{2}$
Giải thích các bước giải:
c) $x.30\%-\dfrac{1}{2}.(x-5) = -\dfrac{2}{5}$
$⇔ x.\dfrac{3}{10} - \dfrac{x}{2}+\dfrac{5}{2} = - \dfrac{2}{5}$
$⇔ \dfrac{3x}{10} - \dfrac{x}{2} = -\dfrac{2}{5}-\dfrac{5}{2}$
$⇔\dfrac{3x-5x}{10} = \dfrac{-4-25}{10}$
$⇔ \dfrac{-2x}{10} = \dfrac{-29}{10}$
$⇔-2x=-29$
$⇔x=\dfrac{29}{2}$
Vậy $x = \dfrac{29}{2}$
