1. Выполните действия: 8/9 - 7/12

1. $\frac{8}{9} - \frac{7}{12} = \frac{32}{36} - \frac{21}{36} = \frac{11}{36}$ 2. $\frac{1}{3} + \frac{19}{30} - \frac{7}{12} = \frac{20}{60} + \frac{38}{60} - \frac{35}{60} = \frac{23}{60}$ 3. $20\frac{3}{29} - 19\frac{1}{2} = 20\frac{6}{58} - 19\frac{29}{58} = 19\frac{64}{58} - 19\frac{29}{58} = \frac{35}{58}$ 4. $4\frac{3}{8} \cdot 5\frac{1}{15} = \frac{35}{8} \cdot \frac{76}{15} = \frac{7}{2} \cdot \frac{19}{3} = \frac{133}{6} = 22\frac{1}{6}$ 5. $6\frac{6}{13} \cdot \frac{1}{2} = \frac{84}{13} \cdot \frac{1}{2} = \frac{42}{13} = 3\frac{3}{13}$ 6. $\frac{2}{3} : \frac{16}{45} = \frac{2}{3} \cdot \frac{45}{16} = \frac{1}{1} \cdot \frac{15}{8} = 1\frac{7}{8}$ 7. $4\frac{1}{10} : 6\frac{1}{2} = \frac{41}{10} : \frac{13}{2} = \frac{41}{10} \cdot \frac{2}{13} = \frac{41}{5} \cdot \frac{1}{13} = \frac{41}{65}$ 8. $85000 \cdot 0.22 = 18700$. Ответ: 18700 пенсионеров. 9. $(1.4 - 4.9) \cdot 1.2 = -3.5 \cdot 1.2 = -4.2$ 10. $-6.8 + 4.5 \cdot 1.4 = -6.8 + 6.3 = -0.5$ 11. $(-8 + 3.8) \cdot 9.5 = -4.2 \cdot 9.5 = -39.9$ 12. $x - 6(x - 3) = x - 6x + 18 = 18 - 5x$. Подставим $x = -7$: $18 - 5(-7) = 18 + 35 = 53$ 13. $-8x = -16 - 8(8x - 9) \Rightarrow -8x = -16 - 64x + 72 \Rightarrow 56x = 56 \Rightarrow x = 1$ 14. $-6(7x + 1) = 6(-2x - 11) \Rightarrow -42x - 6 = -12x - 66 \Rightarrow -30x = -60 \Rightarrow x = 2$ 15. $7x + 4.7 = 6.5x + 9.4 \Rightarrow 0.5x = 4.7 \Rightarrow x = 9.4$