Задание 1. Найдите значение выражения: 1) \(\frac{2}{7}\cdot\frac{42}{5}\); 2) \(\frac{3}{16}:\frac{5}{8}\); 3) \(\frac{1}{10}-\frac{39}{50}\); 4) \(\frac{1}{5}+\frac{3}{20}\).

1. \[\frac{2}{7}\cdot\frac{42}{5}=\frac{2\cdot42}{7\cdot5}=\frac{2\cdot6}{5}=\frac{12}{5}=2\frac{2}{5}.\]
2. \[\frac{3}{16}:\frac{5}{8}=\frac{3}{16}\cdot\frac{8}{5}=\frac{3}{10}.\]
3. \[\frac{1}{10}-\frac{39}{50}=\frac{5}{50}-\frac{39}{50}=-\frac{34}{50}=-\frac{17}{25}.\]
4. \[\frac{1}{5}+\frac{3}{20}=\frac{4}{20}+\frac{3}{20}=\frac{7}{20}.\]

Ответ: 1) \(2\frac{2}{5}\); 2) \(\frac{3}{10}\); 3) \(-\frac{17}{25}\); 4) \(\frac{7}{20}\).