The price of a certain product was reduced by 20% due to unsalable products. Later, the technical department improved the product and turned it into a best-selling product. Now the merchant wants to restore the original price, so how much should the price increase be?
某商品因滞销而降价20%，后来技术部改进产品转为畅销，商家现在要恢复原价那提价了多少．
<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 / (4/5)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">(5/4) - 1</gadget>
<output>1/4 = around 0.25</output>

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