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[latex] \frac{4}{9} : \frac{8}{21}= \frac{4}{9} \cdot \frac{21}{8} = = \frac{4}{3\cdot 3} \cdot \frac{3\cdot 7}{4\cdot 2} = \frac{7}{3\cdot 2} = \frac{7}{6} =1\frac{1}{6}\\\\ \frac{0,42}{9,8} = \frac{42}{980} = \frac{2\cdot 21}{2\cdot 490} = \frac{21}{490} \\\\0,2- \frac{1}{9} = \frac{2}{10} - \frac{1}{9}= \frac{1}{5} - \frac{1}{9} = \frac{9-5}{5\cdot 9} = \frac{4}{45} \\\\4,5: \frac{5}{9}=4 \frac{5}{10} : \frac{5}{9} = 4\frac{1}{2} \cdot \frac{9}{5}= \frac{9}{2} \cdot \frac{9}{5} = \frac{81}{10} =8,1[/latex]