Вычислите: 16/25 * (2/3 + 7/12) - 9/10 : 15/16. Запишите полностью решение и ответ.

18. $\frac{16}{25} \cdot (\frac{2}{3} + \frac{7}{12}) - \frac{9}{10} : \frac{15}{16}$ 1) $\frac{2}{3} + \frac{7}{12} = \frac{8+7}{12} = \frac{15}{12} = \frac{5}{4}$ 2) $\frac{16}{25} \cdot \frac{5}{4} = \frac{4 \cdot 1}{5 \cdot 1} = \frac{4}{5}$ 3) $\frac{9}{10} : \frac{15}{16} = \frac{9}{10} \cdot \frac{16}{15} = \frac{3 \cdot 8}{5 \cdot 5} = \frac{24}{25}$ 4) $\frac{4}{5} - \frac{24}{25} = \frac{20-24}{25} = -\frac{4}{25} = -0,16$ **Ответ: -0,16** 19. $\frac{9}{16} \cdot (\frac{1}{4} + \frac{5}{12}) - \frac{8}{15} : \frac{16}{45}$ 1) $\frac{1}{4} + \frac{5}{12} = \frac{3+5}{12} = \frac{8}{12} = \frac{2}{3}$ 2) $\frac{9}{16} \cdot \frac{2}{3} = \frac{3 \cdot 1}{8 \cdot 1} = \frac{3}{8}$ 3) $\frac{8}{15} : \frac{16}{45} = \frac{8}{15} \cdot \frac{45}{16} = \frac{1 \cdot 3}{1 \cdot 2} = \frac{3}{2}$ 4) $\frac{3}{8} - \frac{3}{2} = \frac{3-12}{8} = -\frac{9}{8} = -1,125$ **Ответ: -1,125** 20. $\frac{4}{3} + (-5\frac{1}{2} + \frac{5}{4} \cdot 3\frac{1}{5}) : \frac{9}{10}$ 1) $\frac{5}{4} \cdot 3\frac{1}{5} = \frac{5}{4} \cdot \frac{16}{5} = \frac{1 \cdot 4}{1 \cdot 1} = 4$ 2) -5\frac{1}{2} + 4 = -5,5 + 4 = -1,5 = -\frac{3}{2} 3) -\frac{3}{2} : \frac{9}{10} = -\frac{3}{2} \cdot \frac{10}{9} = -\frac{1 \cdot 5}{1 \cdot 3} = -\frac{5}{3} 4) $\frac{4}{3} + (-\frac{5}{3}) = -\frac{1}{3}$ **Ответ: -1/3** 21. $\frac{5}{4} + (-7\frac{3}{4} + \frac{7}{4} \cdot 2\frac{2}{7}) : \frac{5}{9}$ 1) $\frac{7}{4} \cdot 2\frac{2}{7} = \frac{7}{4} \cdot \frac{16}{7} = \frac{1 \cdot 4}{1 \cdot 1} = 4$ 2) -7\frac{3}{4} + 4 = -3,75 = -\frac{15}{4} 3) -\frac{15}{4} : \frac{5}{9} = -\frac{15}{4} \cdot \frac{9}{5} = -\frac{3 \cdot 9}{4 \cdot 1} = -\frac{27}{4} 4) $\frac{5}{4} - \frac{27}{4} = -\frac{22}{4} = -5,5$ **Ответ: -5,5**