A commodity is 1,500 yuan, and the current price is 20% off, how much cheaper than the original price.
一件商品1500元，现价八折出售，比原价便宜多少元．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1_500 * (1/5)</gadget>
<output>300</output>

<result>300</result>