Answer
$\frac{1}{5}$
Work Step by Step
Recall that $a^{x/y}=\sqrt[y] {a^x}$. Also recall that the negative exponent rule states that for every nonzero number $a$ and integer $n$, $a^{-n}=\frac{1}{a^n}$.
Use these rules to simplify: $25^{-1/2}=\frac{1}{25^{1/2}}=\frac{1}{\sqrt{25}}=\frac{1}{5}$
