During the Shanghai World Expo, the entrance ticket for a scenic spot in Shanghai is 80 yuan, and it is sold at a 20% discount. How much cheaper is the entrance ticket for this scenic spot?
上海世博会期间，上海某景点的门票为80元，它是按8折出售的，这个景点门票便宜了多少元？
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

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

<gadget id="calculator">100 - 80</gadget>
<output>20</output>

<result>20</result>