Answer
$log _{b} 0.25=6$
Work Step by Step
\[
\begin{array}{l}
Given\ log_{b} 5=10, \log _{b}20=4 \\
\log _{b} 0.25=? \\
\log _{b}\left(\frac{m}{n}\right)=\log _{b} m-\log _{b} n
\end{array}
\]
$P u t \quad m=5, \quad n=20$
\[
\begin{array}{l}
\therefore \log _{b}\left(\frac{5}{20}\right)=\log _{b} 5-\log _{b}20 \\
\Rightarrow \log _{b} 0.25=10-4 \\
\therefore \quad \log _{b} 0.25=6
\end{array}
\]
