a) \(\dfrac{1}{2}\) giờ \(= \dfrac{5}{10}\) giờ \(= 0,5\) giờ ;
\(\dfrac{3}{4}\) giờ \(= \dfrac{75}{100}\) giờ \(= 0,75\) giờ ;
\(\dfrac{1}{4}\) phút \(= \dfrac{25}{100}\) phút \(=0,25\) phút.
b) \(\dfrac{7}{2}m\) \(= \dfrac{35}{10}m=3,5m\) ;
\(\dfrac{3}{10}km=0,3km\) ;
\(\dfrac{2}{5}kg\) \(= \dfrac{4}{10}kg=0,4kg\).