#### Answer

$\frac{1}{400}=.003=.3$%

#### Work Step by Step

We are given the fraction $\frac{1}{400}$.
We know that $\frac{1}{400}=1\div400=.0025\approx.003$
To write $\frac{1}{400}$ as a percentage, we can set $\frac{1}{400}$ equal to $\frac{p}{100}$ (where p is the percentage representation of the given fraction) and take the cross products to solve for p.
$\frac{1}{400}=\frac{p}{100}$
$1\times100=400\times p$
$100=400p$
Divide both sides by 400.
$p=(.25\approx.3)$%
Therefore, $\frac{1}{400}=.003=.3$%.