If $10^{2y} = 25$, then $10^{ - y}$ equals: 
$\textbf{(A)}\ -\frac{1}{5}\qquad \textbf{(B)}\ \frac{1}{625}\qquad \textbf{(C)}\ \frac{1}{50}\qquad \textbf{(D)}\ \frac{1}{25}\qquad \textbf{(E)}\ \frac{1}{5}$
If $10^{2y}=(10^{y})^2 = 25$, then $10^y = 5$ and $10^{-y} = \boxed{\textbf{(E)} \quad \frac{1}{5}}.$