When the price of an item was reduced by 20%, its sale increased by x%. If there is an increase of 25% in receipt of the revenue, then the value of x is:

$$20\% = \frac{1}{5}$$
\[\begin{array}{*{20}{c}} {}&{{\text{Price}}}&{{\text{Total}}}&{{\text{Sales}}}&{} \\ {{\text{Old}} \to }&5&{100}&{\frac{{100}}{5}}&{ = 20} \\ {{\text{New}} \to }&4&{125}&{\frac{{125}}{4}}&{ \,\,\,\,\,\,\, = 31.25} \end{array}\]
$$\eqalign{ & {\text{Increase in sale}} = 31.25 - 20 = 11.25 \cr & {\text{Increase }}\% = \frac{{11.25}}{{20}} \times 100 = 56.25\% \cr} $$