Ta có :
\(\dfrac{4}{5}=\dfrac{140}{175};\dfrac{28}{5}=\dfrac{196}{175};\dfrac{28}{7}=\dfrac{700}{175};\dfrac{25}{25}=\dfrac{175}{175};\dfrac{2}{5}=\dfrac{70}{175}\\ \dfrac{70}{175}< \dfrac{140}{175}< \dfrac{175}{175}< \dfrac{700}{175}< \dfrac{980}{175}\\ \Rightarrow\dfrac{2}{5}< \dfrac{4}{5}< \dfrac{25}{25}< \dfrac{28}{7}< \dfrac{28}{5}\)