\[\boxed{\mathbf{1.}\mathbf{94}}\]
\[\textbf{а)}\frac{90 + 45}{90} \cdot 100\% - 100\% =\]
\[= \frac{135}{90} \cdot 100\% - 100\% =\]
\[= 150\% - 100\% = на\ 50\%.\]
\[\textbf{б)}\ 100\% - \frac{115 - 23}{115} \cdot 100\% =\]
\[= 100\% - \frac{92}{115} \cdot 100\% =\]
\[= 100\% - 80\% = на\ 20\%.\]
\[\textbf{в)}\frac{4a}{a} \cdot 100\% - 100\% =\]
\[= 400\% - 100\% = на\ 300\%.\]
\[\textbf{г)}\ 100\% - \frac{a}{4}\ :a \cdot 100\% =\]
\[= 100\% - \frac{100}{4}\% =\]
\[= 100\% - 25\% = на\ 75\%.\]