\[\boxed{Страница\ 11.}\]
\[\boxed{\mathbf{1.}}\]
\[AB = \frac{3}{5}CD \rightarrow правильная\ часть.\]
\[CD = \frac{5}{3}AB \rightarrow неправильная\ \]
\[часть.\]
\[\boxed{\mathbf{2.}}\]
\[Правильные\ части\ отрезков\ \]
\[(подчеркните\ их\ в\ тетради):\]
\[\frac{4}{5}EF;\ \ \frac{2}{9}MK;\ \ \frac{5}{8}\text{XY.}\]
\[\boxed{\mathbf{3.}}\]
\[AB = 2\ части;\ \ \ CD = 5\ частей;\ \ \text{\ \ }\]
\[EF = 7\ частей.\]
\[AB = \frac{2}{5}\text{CD}\]
\[CD = \frac{5}{2}\text{AB}\]
\[AB = \frac{2}{7}\text{EF}\]
\[EF = \frac{7}{2}\text{AB}\]
\[CD = \frac{5}{7}\text{EF}\]
\[EF = \frac{7}{5}\text{CD}\]
\[\boxed{\mathbf{4.}}\]
\[\frac{20}{4} = 5\]
\[\frac{56}{7} = 8\]
\[\frac{72}{8} = 9\]
\[\frac{42}{6} = 7\]
\[\frac{30}{5} = 6\]
\[\boxed{\mathbf{5.}}\]
\[x + \frac{5}{9} = \frac{7}{9}\]
\[x = \frac{7}{9} - \frac{5}{9}\]
\[x = \frac{2}{9}.\]
\[y - \frac{4}{11} = \frac{6}{11}\]
\[y = \frac{6}{11} + \frac{4}{11}\]
\[y = \frac{10}{11}.\]
\[\frac{12}{10} - n = \frac{8}{10}\]
\[n = \frac{12}{10} - \frac{8}{10}\]
\[n = \frac{4}{10}.\]
\[\boxed{\mathbf{6.}}\]
\[56 = 7 \cdot 8\]
\[48 = 8 \cdot 6\]
\[Число\ 786.\]
\[Два\ числа\ превратились\ в\ \]
\[5648:\ \ \ 56\ и\ 48.\]
\[Ответ:C.\ 2.\]