A dress is priced at 640 yuan, and it is now on sale at a 20% discount. How much is it selling now?
一件连衣裙标价640元，现降20%出售，现卖多少元．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">640 * (4/5)</gadget>
<output>512</output>

<result>512</result>