Приведите дроби \(\frac{7}{8}\), \(\frac{8}{5}\), \(\frac{5}{16}\) и \(\frac{21}{40}\) к знаменателю 80.

1. \(\frac{7}{8}=\frac{7\cdot10}{8\cdot10}=\frac{70}{80}\).
2. \(\frac{8}{5}=\frac{8\cdot16}{5\cdot16}=\frac{128}{80}\).
3. \(\frac{5}{16}=\frac{5\cdot5}{16\cdot5}=\frac{25}{80}\).
4. \(\frac{21}{40}=\frac{21\cdot2}{40\cdot2}=\frac{42}{80}\).

Ответ: \(\frac{70}{80},\ \frac{128}{80},\ \frac{25}{80},\ \frac{42}{80}\).