A jacket is 100 yuan, how much is the price after 20% off?
一件上衣100元，打八折以后的价钱是多少元钱．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">100 * (4/5)</gadget>
<output>80</output>

<result>80</result>