The original price of a commodity is 280 yuan, and now it is sold at a 30% discount, which is how much cheaper.
一件商品原价280元，现打七折出售，便宜了多少元．
<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 - (7/10)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">280 * (3/10)</gadget>
<output>84</output>

<result>84</result>