Answer
-1
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, $log \frac{1}{10}=log_{10}\frac{1}{10}=-1$. We know this, because $10^{-1}=\frac{1}{10^{1}}=\frac{1}{10}$.
