\[\boxed{\mathbf{Задание\ №5\ «Проверь\ себя»}\mathbf{\text{.\ }}Еуроки\ - \ ДЗ\ без\ мороки}\]
\[\boxed{\mathbf{1.\ }}\]
\[\frac{72}{90} = \frac{72\ :9}{90\ :9} = \frac{8}{10}\]
\[Ответ:Б).\]
\[\boxed{\mathbf{2.\ }}\]
\[16 + 12 = 28\ (учеников) -\]
\[всего\ в\ классе.\]
\[16\ :28 = \frac{16}{28} = \frac{4}{7}\ (часть) -\]
\[учащихся\ посещает\]
\[математический\ кружок.\]
\[Ответ:А).\]
\[\boxed{\mathbf{3.\ }}\]
\[14\ ч\ 30\ мин - 13\ ч\ 50\ мин =\]
\[13\ ч\ 90\ мин - 13\ ч\ 50\ мин =\]
\[= 40\ (мин) - прошло.\]
\[40\ :60 = \frac{40}{60} = \frac{2}{3}(часть) -\]
\[часа\ прошла.\]
\[Ответ:В).\]
\[\boxed{\mathbf{4.\ }}\]
\[\frac{42}{60} = \frac{7}{a}\]
\[\frac{7}{10} = \frac{7}{a}\]
\[a = 10.\]
\[Ответ:В).\]
\[\boxed{\mathbf{5.\ }}\]
\[\frac{2}{4} = \frac{1}{2};\ \frac{2}{5};\ \frac{2}{6} = \frac{1}{3};\ \frac{2}{8} = \frac{1}{4};\ \frac{2}{9};\]
\[\frac{4}{5};\ \frac{4}{6} = \frac{2}{3};\ \frac{4}{8} = \frac{1}{2};\ \frac{4}{9};\ \frac{5}{6};\ \frac{5}{8};\]
\[\frac{5}{9};\ \frac{6}{8} = \frac{3}{4};\ \frac{6}{9} = \frac{2}{3};\ \frac{8}{9}.\]
\[Неравных\ дробей\ 13.\]
\[Ответ:Б).\]
\[\boxed{\mathbf{6.\ }}\]
\[А)\ \frac{2}{3} = \frac{4}{6} < \frac{5}{6}\]
\[Ответ:А).\]
\[\boxed{\mathbf{7.\ }}\]
\[\frac{x}{9} < \frac{19}{36}\]
\[\frac{4x}{36} < \frac{19}{36}\]
\[x = 1;2;3;4.\]
\[Ответ:В).\]
\[\boxed{\mathbf{8.\ }}\]
\[\frac{3}{8} < \frac{x}{24} < \frac{2}{3}\]
\[\frac{9}{24} < \frac{x}{24} < \frac{16}{24}\]
\[x = 10;11;12;13;14;15.\]
\[Всего\ 6\ дробей.\]
\[Ответ:Г).\]
\[\boxed{\mathbf{9.\ }}\]
\[\frac{7^{\backslash 6}}{15} + \frac{4^{\backslash 10}}{9} - \frac{3^{\backslash 9}}{10} =\]
\[= \frac{42 + 40 - 27}{90} = \frac{55}{90} = \frac{11}{18}.\]
\[Ответ:Б).\]
\[\boxed{\mathbf{10.\ }}\]
\[5\frac{7^{\backslash 2}}{9} - 3\frac{5^{\backslash 3}}{6} = 5\frac{14}{18} - 3\frac{15}{18} =\]
\[= 4\frac{32}{18} - 3\frac{15}{18} = 1\frac{17}{18}.\]
\[Ответ:В).\]
\[\boxed{\mathbf{11.\ }}\]
\[\frac{13}{21} - \left( x - 2\frac{5}{7} \right) = \frac{3}{14}\]
\[x - 2\frac{5}{7} = \frac{13^{\backslash 2}}{21} - \frac{3^{\backslash 3}}{14}\]
\[x - 2\frac{5}{7} = \frac{26}{42} - \frac{9}{42}\]
\[x - 2\frac{5^{\backslash 6}}{7} = \frac{17}{42}\]
\[x = \frac{17}{42} + 2\frac{30}{42}\]
\[x = 2\frac{47}{42} = 3\frac{5}{42}.\]
\[Ответ:Г).\]
\[\boxed{\mathbf{12.\ }}\]
\[1 - \frac{1}{2} = \frac{1}{2}\ (часть) - яблок\]
\[осталась.\]
\[1 - \frac{1}{3} = \frac{2}{3}\ (часть) - груш\]
\[осталась.\]
\[1 + 1 = 2 - все\ фрукты.\]
\[\frac{1^{\backslash 3}}{2} + \frac{2^{\backslash 2}}{3} = \frac{3}{6} + \frac{4}{6} = \frac{7}{6} =\]
\[= 1\frac{1}{2}\ (часть) - фруктов\ \]
\[осталась.\]
\[Значит,\ осталось\ больше\ \]
\[половины\ фруктов.\]
\[Ответ:Б).\]