If x% of a is the same as y% of b, then z% of b is :

Answer: Option C

$$\begin{array}{rl}& x\%\text{ of }a=y\%\text{ of }a\\ & \Rightarrow \frac{x}{100}a=\frac{y}{100}b\\ & \Rightarrow b=\left(\frac{x}{y}\right)a\\ & \therefore z\%\text{ of }b:\\ & =\left(z\%\text{ of }\frac{x}{y}\right)a\\ & =\left(\frac{xz}{y\times 100}\right)a\\ & =\left(\frac{xz}{y}\right)\%\text{ of }a\end{array}$$