11.
[tex]a)\\1\frac{2}{3}\cdot\frac{9}{14} = \frac{5}{3}\cdot\frac{9}{14} = 5\cdot\frac{3}{14} = \frac{15}{14} = 1\frac{1}{14}\\\\4\frac{3}{18}\cdot9 = \frac{75}{18}\cdot9 = \frac{75}{2} = 37\frac{1}{2}[/tex]
[tex]b)\\12\cdot3\frac{1}{6} = 12\cdot\frac{19}{6} = 2\cdot19 = 38\\\\2\frac{1}{4}\cdot2\frac{2}{7} = \frac{9}{4}\cdot\frac{16}{7} = 9\cdot\frac{4}{7} = \frac{36}{7} = 5\frac{1}{7}[/tex]
12.
[tex]a)\\\frac{7}{8}:3 = \frac{7}{8}\cdot\frac{1}{3} = \frac{7}{24}\\\\5:2\frac{1}{4} = 5:\frac{9}{4} = 5\cdot\frac{4}{9} = \frac{20}{9} = 2\frac{2}{9}\\\\7\frac{1}{4}:9 = \frac{29}{4}\cdot\frac{1}{9} =\frac{29}{36}[/tex]
[tex]b)\\\frac{2}{5}:\frac{3}{4} = \frac{2}{5}\cdot\frac{4}{3} = \frac{8}{15}\\\\4\frac{3}{8}:\frac{2}{3} = \frac{35}{8}\cdot\frac{3}{2} = \frac{105}{16} = 6\frac{9}{16}\\\\1\frac{1}{3}:1\frac{4}{5} = \frac{4}{3}:\frac{9}{5} = \frac{4}{3}\cdot\frac{5}{9} = \frac{20}{27}[/tex]
