If a product is sold for 400 yuan at 20% off the original price, how much money can be saved by purchasing this product?
某商品按原价的8折出售为400元，则购买该商品可节省多少元．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">400 / (4/5)</gadget>
<output>500</output>

<gadget id="calculator">500 - 400</gadget>
<output>100</output>

<result>100</result>