\(\frac{1}{2}+\frac{1}{4}-\frac{1}{5}=\frac{10}{20}+\frac{5}{20}-\frac{4}{20}=\frac{10+5-4}{20}=\frac{11}{20}\)
\(\frac{1}{2}\times\frac{2}{5}\div\frac{1}{4}=\frac{1}{2}\times\frac{2}{5}\times\frac{4}{1}=\frac{1\times2\times4}{2\times5\times1}=\frac{8}{10}=\frac{4}{5}\)