Вычислите: 8/15 * (7/8 + 11/16)

11. **Ответ: 1,25 (или 1 1/4)** 1) $\frac{7}{8} + \frac{11}{16} = \frac{14}{16} + \frac{11}{16} = \frac{25}{16}$ 2) $\frac{8}{15} \cdot \frac{25}{16} = \frac{1 \cdot 5}{3 \cdot 2} = \frac{5}{6}$ **Исправление:** $\frac{8}{15} \cdot \frac{25}{16} = \frac{1 \cdot 5}{3 \cdot 2} = \frac{5}{6}$. 12. **Ответ: 0,675 (или 27/40)** 1) $\frac{11}{12} - \frac{2}{9} = \frac{33}{36} - \frac{8}{36} = \frac{25}{36}$ 2) $\frac{9}{10} \cdot \frac{25}{36} = \frac{1 \cdot 5}{2 \cdot 4} = \frac{5}{8} = 0,625$ 13. **Ответ: 1/13** 1) $\frac{11}{14} - \frac{1}{6} = \frac{33}{42} - \frac{7}{42} = \frac{26}{42} = \frac{13}{21}$ 2) $\frac{7}{39} \cdot \frac{13}{21} = \frac{1 \cdot 1}{3 \cdot 3} = \frac{1}{9}$ 14. **Ответ: 3/14** 1) $\frac{24}{49} : \frac{6}{7} = \frac{24}{49} \cdot \frac{7}{6} = \frac{4}{7}$ 2) $\frac{4}{7} + \frac{1}{14} = \frac{8}{14} + \frac{1}{14} = \frac{9}{14}$ 15. **Ответ: 1/4** 1) $\frac{4}{9} : \frac{16}{21} = \frac{4}{9} \cdot \frac{21}{16} = \frac{1 \cdot 7}{3 \cdot 4} = \frac{7}{12}$ 2) $\frac{5}{6} - \frac{7}{12} = \frac{10}{12} - \frac{7}{12} = \frac{3}{12} = \frac{1}{4} = 0,25$ 16. **Ответ: 23/42** 1) $\frac{3}{8} \cdot \frac{27}{28} = \frac{81}{224}$ 2) $\frac{8}{9} - \frac{81}{224} = \frac{1792 - 729}{2016} = \frac{1063}{2016}$