The original price of a commodity is 100 yuan, and now it is sold at a 20% discount. How much is it cheaper now?
一种商品原价是100元，现在打八折销售，现在便宜了多少元．
<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">100 * (1/5)</gadget>
<output>20</output>

<result>20</result>