If the price of a product is reduced by 20% during the promotion period, and then increased by 20% after the promotion, the price of the product at this time is the original price.
某商品在促销时期降价20%，促销过后又涨20%，这时商品的价格是原来价格的多少．
<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 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">(6/5) / 1</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">1 * (4/5) * (6/5)</gadget>
<output>24/25 = around 0.96</output>

<result>24/25 = around 0.96</result>