7. Вычислите разность.

Решение:

1. \( \frac{7}{8} - \frac{3}{4} = \frac{7}{8} - \frac{6}{8} = \frac{1}{8} \)
2. \( \frac{9}{10} - \frac{2}{5} = \frac{9}{10} - \frac{4}{10} = \frac{5}{10} = \frac{1}{2} \)
3. \( \frac{3}{5} - \frac{4}{15} = \frac{9}{15} - \frac{4}{15} = \frac{5}{15} = \frac{1}{3} \)
4. \( \frac{7}{8} - \frac{6}{7} = \frac{49}{56} - \frac{48}{56} = \frac{1}{56} \)
5. \( \frac{7}{12} - \frac{8}{15} = \frac{35}{60} - \frac{32}{60} = \frac{3}{60} = \frac{1}{20} \)
6. \( \frac{25}{39} - \frac{15}{26} = \frac{50}{78} - \frac{45}{78} = \frac{5}{78} \)
7. \( \frac{7}{15} - \frac{8}{25} = \frac{35}{75} - \frac{24}{75} = \frac{11}{75} \)
8. \( \frac{7}{45} - \frac{7}{60} = \frac{28}{180} - \frac{21}{180} = \frac{7}{180} \)

Ответ: \( \frac{1}{8}, \frac{1}{2}, \frac{1}{3}, \frac{1}{56}, \frac{1}{20}, \frac{5}{78}, \frac{11}{75}, \frac{7}{180} \).