A commodity is priced at 300 yuan with a 20% discount, which is how much cheaper than the original price.
一种商品，打八折售价为300元，比原价便宜多少元．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">300 / (4/5)</gadget>
<output>375</output>

<gadget id="calculator">375 - 300</gadget>
<output>75</output>

<result>75</result>