$答:\frac{3}{4}:\frac{1}{2}=2.4: 1.6~~~~\frac{3}{4}: 2.4=\frac{1}{2}:1.6\ $
$1.6:\frac{1}{2}=2.4:\frac{3}{4}~~~~1.6:2.4=\frac{1}{2}:\frac{3}{4}\ $
$\frac{1}{2} :\frac{3}{4}=1.6: 2.4~~~~ \frac{1}{2} :1.6=\frac{3}{4} :2.4\ $
$2.4:\frac{3}{4}=1.6:\frac{1}{2}~~~~2.4: 1.6=\frac{3}{4}: \frac{1}{2}\ $