Решение:
\[ \frac{1}{5} = \frac{1 \times 4}{5 \times 4} = \frac{4}{20} \]
\[ \frac{3}{4} = \frac{3 \times 5}{4 \times 5} = \frac{15}{20} \]
\[ \frac{4}{20} - \frac{15}{20} = \frac{4 - 15}{20} = \frac{-11}{20} \]
Ответ: -11/20