$\frac{1}{2}$ + $\frac{1}{4}$ - $\frac{1}{5}$
= $\frac{4}{8}$ + $\frac{2}{8}$ - $\frac{1}{5}$
= $\frac{3}{4}$ - $\frac{1}{5}$
= $\frac{15}{20}$ - $\frac{4}{20}$
= $\frac{11}{20}$
$\frac{1}{2}$ x $\frac{2}{5}$ : $\frac{1}{4}$
= $\frac{1}{5}$ : $\frac{1}{4}$
= $\frac{1}{5}$ : $\frac{1}{4}$
= $\frac{1}{5}$ x $\frac{4}{1}$
= $\frac{4}{5}$