$75\div 100=\dfrac{3}{4}\left(元\right)；$
$500\div 1000=\dfrac{1}{2}\left(吨\right)；$
$40\div 60=\dfrac{2}{3}\left(分\right)；$
$1400\div 1000=\dfrac{7}{5}\left(\mathrm{千克}\right)；$
$0.25\times 60=15\left(分\right)$
7.5×60=450(秒)
$故答案为：\dfrac{3}{4}；\dfrac{1}{2}；\dfrac{2}{3}；\dfrac{7}{5}；15；450。$
