Answer
-3
Work Step by Step
A common logarithm is a logarithm to base 10. As shown on page 580, when a common logarithm is written in the form $log (x)$, this is equivalent to the expression $log_{10}x$.
Therefore, $log \frac{1}{1000}=log_{10}\frac{1}{1000}=-3$. We know this, because $10^{-3}=\frac{1}{10^{3}}=\frac{1}{10\times10\times10}=\frac{1}{1000}$.
