"x" being the 100%, now if it decreased by 5%, this week's rain was 100% - 5% = 95% of last week's.
[tex]\bf \begin{array}{|c|ll} \cline{1-1} \textit{a\% of b}\\ \cline{1-1} \\ \left( \cfrac{a}{100} \right)\cdot b \\\\ \cline{1-1} \end{array}~\hspace{5em}\stackrel{\textit{95\% of \underline{x}}}{\left( \cfrac{95}{100} \right)x}\implies 0.95x[/tex]
