1250. Вычислите: 1) (-3/14 - 8/21) : 20/21; 2) 3/8 : (-5/8) - (-2 1/4) : (-1 4/11); 3) (-4 1/12 + 3 9/10) : 3 3/10; 4) (11/14 - 5/6) : (11/14 - 3/4).

1) $(-\frac{3}{14} - \frac{8}{21}) : \frac{20}{21} = (-\frac{9}{42} - \frac{16}{42}) : \frac{20}{21} = -\frac{25}{42} \cdot \frac{21}{20} = -\frac{5 \cdot 5 \cdot 21}{2 \cdot 21 \cdot 4 \cdot 5} = -\frac{5}{8}$ 2) $\frac{3}{8} : (-\frac{5}{8}) - (-2\frac{1}{4}) : (-1\frac{4}{11}) = \frac{3}{8} \cdot (-\frac{8}{5}) - (-\frac{9}{4}) : (-\frac{15}{11}) = -\frac{3}{5} - (\frac{9}{4} \cdot \frac{11}{15}) = -\frac{3}{5} - \frac{3 \cdot 11}{4 \cdot 5} = -\frac{12}{20} - \frac{33}{20} = -\frac{45}{20} = -2\frac{5}{20} = -2\frac{1}{4} = -2,25$ 3) (-4$\frac{1}{12}$ + 3$\frac{9}{10}$) : 3$\frac{3}{10}$ = (-$\frac{49}{12}$ + $\frac{39}{10}$) : $\frac{33}{10}$ = (-$\frac{245}{60}$ + $\frac{234}{60}$) : $\frac{33}{10}$ = -$\frac{11}{60} \cdot \frac{10}{33} = -\frac{11 \cdot 10}{6 \cdot 10 \cdot 3 \cdot 11} = -\frac{1}{18}$ 4) ($\frac{11}{14}$ - $\frac{5}{6}$) : ($\frac{11}{14}$ - $\frac{3}{4}$) = ($\frac{33}{42}$ - $\frac{35}{42}$) : ($\frac{22}{28}$ - $\frac{21}{28}$) = -$\frac{2}{42} : \frac{1}{28} = -\frac{1}{21} \cdot 28 = -\frac{28}{21} = -1\frac{7}{21} = -1\frac{1}{3}$ **Ответ:** 1) $-5/8$; 2) $-2,25$; 3) $-1/18$; 4) $-1\frac{1}{3}$.