Tìm x, biết:

a) $x \times \frac{21}{25} = \frac{- 7}{10}$ suy ra $x = (\frac{- 7}{10} / \frac{21}{25} = \frac{- 5}{6}$

b) $\frac{- 3}{20} x = \frac{5}{12} - \frac{2}{5}$ suy ra $x = \frac{1}{60} / (\frac{- 3}{20}) = \frac{- 1}{9}$

c) $\frac{2}{9} / x = \frac{1}{18} / 0.375$ suy ra $x = \frac{2}{9} / \frac{4}{27} = \frac{3}{2}$

d) $(- \frac{11}{12}) / 2 x = \frac{5}{2} + \frac{1}{4}$

$(- \frac{11}{12}) / 2 x = \frac{11}{4}$ suy ra $2 x = (\frac{- 11}{12}) / \frac{11}{4}$ nên $x = \frac{- 1}{6}$