Ответ:
\[\frac{7}{10}+\frac{17}{40}=\frac{28}{40}+\frac{17}{40}=\frac{45}{40}=\frac{9}{8}.\]
\[\frac{9}{10}:\frac{9}{8}=\frac{9}{10}\cdot\frac{8}{9}=\frac{4}{5}.\]
Ответ: \(\frac{4}{5}\).
\[\frac{7}{10}+\frac{17}{40}=\frac{28}{40}+\frac{17}{40}=\frac{45}{40}=\frac{9}{8}.\]
\[\frac{9}{10}:\frac{9}{8}=\frac{9}{10}\cdot\frac{8}{9}=\frac{4}{5}.\]
Ответ: \(\frac{4}{5}\).