The current price of a commodity is 80 yuan, which is 20% lower than that in the past. What is the correct list of the past price?
一种商品，现价80元，比过去降低了20%，求过去价格的正确列式是多少．
<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">80 / (4/5)</gadget>
<output>100</output>

<result>100</result>