Bài 1 :
\(a,\dfrac{8}{7}:\dfrac{4}{9}=\dfrac{8}{7}\times\dfrac{9}{4}=\dfrac{36}{28}\)
\(b,\dfrac{5}{8}:\dfrac{5}{16}=\dfrac{5}{8}\times\dfrac{16}{5}=\dfrac{80}{40}\)
\(c,\dfrac{3}{7}:5=\dfrac{3}{7}\times\dfrac{1}{5}=\dfrac{3}{35}\)
\(d,4:\dfrac{2}{7}=\dfrac{4}{1}\times\dfrac{7}{2}=\dfrac{28}{2}\)
\(\)Bài 2 :
\(a,\dfrac{a}{b}\times\dfrac{1}{3}=\dfrac{5}{6}\) \(b,\dfrac{4}{5}\times\dfrac{a}{b}=\dfrac{7}{9}\)
\(\dfrac{a}{b}=\dfrac{5}{6}:\dfrac{1}{3}=\dfrac{15}{6}\) \(\dfrac{a}{b}=\dfrac{7}{9}:\dfrac{4}{5}=\dfrac{35}{36}\)
\(c,\dfrac{8}{5}:\dfrac{a}{b}=\dfrac{4}{9}\) \(d,4:\dfrac{a}{b}=\dfrac{2}{7}\)
\(\dfrac{a}{b}=\dfrac{8}{5}:\dfrac{4}{9}=\dfrac{72}{20}\) \(\dfrac{a}{b}=4:\dfrac{2}{7}=\dfrac{28}{2}\)