we certainly could do so IF only IF the proportion of 12 and 2 are at the same ratio as 1½ and 1/3, namely if both yield the same fraction, let's see, and firstly converting the mixed fraction to improper.
[tex]\bf \cfrac{12}{2}=\cfrac{~~1\frac{1}{2}~~}{\frac{1}{3}}\implies 6=\cfrac{~~\frac{1\cdot 2+1}{2}~~}{\frac{1}{3}}\implies 6=\cfrac{~~\frac{3}{2}~~}{\frac{1}{3}}\implies 6=\cfrac{3}{2}\cdot \cfrac{3}{1}\implies 6\ne \cfrac{9}{2}~~\bigotimes[/tex]
