The price of a fountain pen is 20 yuan after the price is reduced by 20%. What is the original price of this fountain pen?
一种钢笔降价20%后售价是20元，这种钢笔原价是多少元．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">20 / (4/5)</gadget>
<output>25</output>

<result>25</result>