Ответ:
\[\frac{7}{10}:\left(\frac{3}{8}-\frac{1}{5}\right)=\frac{7}{10}:\left(\frac{15}{40}-\frac{8}{40}\right)=\frac{7}{10}:\frac{7}{40}=\frac{7}{10}\cdot\frac{40}{7}=4.\]
Ответ: 4.
\[\frac{7}{10}:\left(\frac{3}{8}-\frac{1}{5}\right)=\frac{7}{10}:\left(\frac{15}{40}-\frac{8}{40}\right)=\frac{7}{10}:\frac{7}{40}=\frac{7}{10}\cdot\frac{40}{7}=4.\]
Ответ: 4.