Tìm x: a) 2/3:x = 2,4 -4/5; 

a) \[\frac{2}{3}:x = 2,4 - \frac{4}{5}\]

\[\frac{2}{3}:x = \frac{{12}}{5} - \frac{4}{5}\]

\[\frac{2}{3}:x = \frac{8}{5}\]

\[x = \frac{2}{3}:\frac{8}{5}\]

\[x = \frac{5}{{12}}\].

Vậy \[x = \frac{5}{{12}}\].

b) \[\frac{5}{4}.\left( {x - \frac{3}{5}} \right) = \frac{{ - 1}}{8}\]

\[x - \frac{3}{5} = \frac{{ - 1}}{8}:\frac{5}{4}\]

\[x - \frac{3}{5} = \frac{{ - 1}}{{10}}\]

\[x = \frac{{ - 1}}{{10}} + \frac{3}{5}\]

\[x = \frac{1}{2}\].

Vậy \[x = \frac{1}{2}\].