A 20% discount on a commodity is the same as a price reduction of 100 yuan. What is the original price of this commodity?
一种商品打八折和降价100元的售价一样，这种商品的原价是多少元．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">100 / (1/5)</gadget>
<output>500</output>

<result>500</result>