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[tex]a.\ \dfrac{20}{27}-\dfrac{7}{9}=\dfrac{20}{27}-\dfrac{3\times7}{3\times9}\\\\\dfrac{20}{27}-\dfrac{7}{9}=\dfrac{20}{27}-\dfrac{21}{27}\\\\\dfrac{20}{27}-\dfrac{7}{9}=-\dfrac{1}{27}\\\\\dfrac{20}{27}-\dfrac{7}{9}<0\\\\\dfrac{20}{27}<\dfrac{7}{9} [/tex]
[tex]b.\ \dfrac{3}{5}-\dfrac{11}{15}=\dfrac{3\times3}{3\times5}-\dfrac{11}{15}\\\\\dfrac{3}{5}-\dfrac{11}{15}=\dfrac{9}{15}-\dfrac{11}{15}\\\\\dfrac{3}{5}-\dfrac{11}{15}=-\dfrac{2}{15}\\\\\dfrac{3}{5}-\dfrac{11}{15}<0\\\\\dfrac{3}{5}<\dfrac{11}{15} [/tex]
[tex]a.\ \dfrac{20}{27}-\dfrac{7}{9}=\dfrac{20}{27}-\dfrac{3\times7}{3\times9}\\\\\dfrac{20}{27}-\dfrac{7}{9}=\dfrac{20}{27}-\dfrac{21}{27}\\\\\dfrac{20}{27}-\dfrac{7}{9}=-\dfrac{1}{27}\\\\\dfrac{20}{27}-\dfrac{7}{9}<0\\\\\dfrac{20}{27}<\dfrac{7}{9} [/tex]
[tex]b.\ \dfrac{3}{5}-\dfrac{11}{15}=\dfrac{3\times3}{3\times5}-\dfrac{11}{15}\\\\\dfrac{3}{5}-\dfrac{11}{15}=\dfrac{9}{15}-\dfrac{11}{15}\\\\\dfrac{3}{5}-\dfrac{11}{15}=-\dfrac{2}{15}\\\\\dfrac{3}{5}-\dfrac{11}{15}<0\\\\\dfrac{3}{5}<\dfrac{11}{15} [/tex]