In the expression $xy^2$, the values of $x$ and $y$ are each decreased $25$ %; the value of the expression is: 
$\textbf{(A)}\ \text{decreased } 50\% \qquad \textbf{(B)}\ \text{decreased }75\%\\  \textbf{(C)}\ \text{decreased }\frac{37}{64}\text{ of its value}\qquad \textbf{(D)}\ \text{decreased }\frac{27}{64}\text{ of its value}\\ \textbf{(E)}\ \text{none of these}$
$xy^2$
$(\frac{3}{4}x)(\frac{3}{4}y)^2$
$(\frac{3}{4})^3xy^2$
$\frac{27}{64}xy^2$
$xy^2-\frac{27}{64}xy^2 = \frac{37}{64}xy^2 \implies \textbf{(C)}$