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[tex]1\frac{5}{7}+\frac{4}{7}=1\frac{9}{7}=1+\frac{9}{7}=1+1\frac{2}{7}=2\frac{2}{7}\\\\2\frac{2}{3}+1\frac{1}{5}=2\frac{2\cdot5}{3\cdot5}+1\frac{1\cdot3}{5\cdot3}=2\frac{10}{15}+1\frac{3}{15}=3\frac{13}{15}\\\\1\frac{4}{13}-\frac{9}{13}=\frac{1\cdot13+4}{13}-\frac{9}{13}=\frac{13+4}{13}-\frac{9}{13}=\frac{17}{13}-\frac{9}{13}=\frac{8}{13}\\\\6\frac{8}{9}-4\frac{2}{3}=6\frac{8}{9}-4\frac{2\cdot3}{3\cdot3}=6\frac{8}{9}-4\frac{6}{9}=2\frac{2}{9}[/tex]
