[tex]\displaystyle
\frac{a}{b}= \frac{2}{5} \\ \\
\frac{4a-b}{a-2b} = ~~(simplificam~fortat ~cu~b) \\ \\
=\frac{ \frac{4a}{b} - \frac{b}{b}}{ \frac{a}{b}- \frac{2b}{b}} = \\ \\
=\frac{ 4\frac{2}{5} - 1}{ \frac{2}{5}- 2} = \frac{ \frac{3}{5}}{ \frac{-8}{5}} = \frac{3}{5}}\times \frac{5}{-8} =\boxed {- \frac{3}{8} }[/tex]
