\(a.=\dfrac{21}{7}-\dfrac{11}{7}=\dfrac{20}{7};b.=\dfrac{13}{18}-\dfrac{9}{18}=\dfrac{4}{18}=\dfrac{2}{9}\\ c.=\dfrac{28}{45};d.=\dfrac{15}{7\times9}=\dfrac{15}{63}\)
\(a,\\ =\dfrac{21}{7}-\dfrac{11}{7}=\dfrac{10}{7}\\ b,\\ =\dfrac{13}{18}-\dfrac{9}{18}=\dfrac{4}{18}=\dfrac{2}{9}\\ c,\\ =\dfrac{28}{45}\\ d,\\ =\dfrac{15}{7}\times\dfrac{1}{9}=\dfrac{15}{63}=\dfrac{5}{21}\)
a=\(\dfrac{10}{7}\) b=\(\dfrac{2}{9}\) c=\(\dfrac{28}{45}\) d=\(\dfrac{5}{21}\)
\(a,3-\dfrac{11}{7}=\dfrac{21}{7}-\dfrac{11}{7}=\dfrac{10}{7}\\ b,\dfrac{13}{18}-\dfrac{3}{6}=\dfrac{13}{18}-\dfrac{9}{18}=\dfrac{4}{18}=\dfrac{2}{9}\\ c,\dfrac{4}{9}\text{×}\dfrac{7}{5}=\dfrac{35}{45}=\dfrac{7}{9}\\ d,\dfrac{15}{7}:9=\dfrac{15}{7}\text{×}\dfrac{1}{9}=\dfrac{15}{63}=\dfrac{5}{21}\)