- \(\frac{2}{7}+\frac{42}{5}=\frac{10+294}{35}=\frac{304}{35}=8\frac{24}{35}\).
- \(\frac{3}{16}\cdot\frac{5}{8}=\frac{15}{128}\).
- \(\frac{1}{10}-\frac{39}{50}=\frac{5-39}{50}=-\frac{34}{50}=-\frac{17}{25}\).
- \(\frac{1}{5}+\frac{3}{20}=\frac{4+3}{20}=\frac{7}{20}\).
Ответ: 1) \(8\frac{24}{35}\); 2) \(\frac{15}{128}\); 3) \(-\frac{17}{25}\); 4) \(\frac{7}{20}\).