To make a 50% solution of carbon tetrachloride in benzene, how much carbon tetrachloride should be added to 100*mL of benzene?

Surely you should add $100 \cdot m L$ of $\text{carbon tetrachloride}$?
You want a 50% $\frac{v}{v}$ solution of $\text{carbon tet}$ in $\text{benzene}$. Clearly, we should take EQUAL volumes of each solvent to prepare such a concentration. You started with a $100 \cdot m L$ of benzene; you thus need a $100 \cdot m L$ volume of carbon tetrachloride. The volumes should certainly be additive to a first approximation.
Could I prepare a 50% solution of $\text{carbon tet}$ in water? Why or why not?