Tìm số hữu tỉ x, biết

a) $x + (- \frac{2}{5}) = \frac{- 1}{3}$

$x = \frac{- 1}{3} - (- \frac{2}{5})$

$x = \frac{1}{15}$ .

b) $0.5 - x = \frac{- 5}{14}$

$x = 0.5 - \frac{- 5}{14}$

$x = \frac{6}{7}$

c) $(- 0.4) \times (2 x + \frac{2}{5}) = - 9.4$

$2 x = [- 9.4 / (- 0.4)] - \frac{2}{5}$

$2 x = \frac{231}{10}$

$x = \frac{231}{20}$

d) $(\frac{3}{2} - x) / \frac{- 14}{3} = \frac{- 6}{7} .$

$\frac{3}{2} - x = \frac{- 6}{7} \times \frac{- 14}{3}$

$\frac{3}{2} - x = 4$

$x = \frac{3}{2} - 4 = \frac{- 5}{2}$