$a) 10x -12x = -20$
$⇔ -2x = -20$
$⇔ x = 10$
Vậy $x=10$
$b) (3x+5).2 = 30$
$⇔ 3x + 5 = 15$
$⇔ 3x = 10$
$⇔ x = \dfrac{10}{3}$
Vậy $x = \dfrac{10}{3}$
$c) (\dfrac{2}{3}.x - \dfrac{1}{2}) . \dfrac{3}{4} - \dfrac{2}{5} .x = 4\dfrac{1}{4}$
$⇔ \dfrac{1}{2}.x - \dfrac{3}{8} - \dfrac{2}{5}x = \dfrac{17}{4}$
$⇔ (\dfrac{1}{2}-\dfrac{2}{5}).x = \dfrac{34}{8} + \dfrac{3}{8}$
$⇔ \dfrac{1}{10}.x = \dfrac{37}{8}$
$⇔ x = \dfrac{37}{8} .10$
$⇔ x = \dfrac{185}{4}$
$d) \dfrac{-2}{3} + \dfrac{5}{12} < x ≤ 4 - \dfrac{1}{3} : \dfrac{1}{6}$
$⇔ \dfrac{-8}{12} + \dfrac{5}{12} < x ≤ 4 - \dfrac{1}{3} . 6$
$⇔ \dfrac{-1}{4} < x ≤ 4-2$
$⇔ \dfrac{-1}{4} < x ≤ 2$
Vậy $\dfrac{-1}{4} < x ≤ 2$
