Ta có:
\(\dfrac{15}{25}\) = \(\dfrac{15:5}{25:5}\) = \(\dfrac{3}{5}\) ; \(\dfrac{9}{15}\) = \(\dfrac{9:3}{15:3}\) = \(\dfrac{3}{5}\) ;
\(\dfrac{20}{32}\) = \(\dfrac{20:4}{32:4}\) = \(\dfrac{5}{8}\) ; \(\dfrac{21}{35}\) = \(\dfrac{21:7}{35:7}\) = \(\dfrac{3}{5}\) ;
Vậy: \(\dfrac{3}{5}\) = \(\dfrac{15}{25}\) = \(\dfrac{9}{15}\) = \(\dfrac{21}{35}\); \(\dfrac{5}{8}\) = \(\dfrac{20}{32}\).
