The price of a product is reduced by 20% due to poor sales, and after improving the process, it becomes a bestseller. How much should the price be increased if the original price is to be restored
某商品因销路不好降价20%，改进工艺后，转为畅销品．如果要恢复原价，价格应提高多少
<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">(1/5) / (4/5)</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>