Vì \(\dfrac{a}{b}=\dfrac{3}{7};\dfrac{c}{b}=\dfrac{15}{28}\)
\(\Rightarrow\dfrac{a}{b}:\dfrac{c}{b}=\dfrac{3}{7}:\dfrac{15}{28}\)
\(\Rightarrow\dfrac{a}{c}=\dfrac{4}{5}\)
\(\Rightarrow\) Tỉ số giữa c và a là \(\dfrac{5}{4}\)
Vì \(\dfrac{a}{b}=\dfrac{3}{7};\dfrac{c}{b}=\dfrac{15}{28}\)
\(\Rightarrow\dfrac{a}{b}:\dfrac{c}{b}=\dfrac{3}{7}:\dfrac{15}{28}\)
\(\Rightarrow\dfrac{a}{c}=\dfrac{4}{5}\)
Vậy ...................