A bicycle costs 500 yuan and is sold at a 20% discount. How much is Xiao Ming cheaper in buying this bicycle?
一辆自行车500元，打八折出售，小明买这辆车便宜了多少钱？
<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">500 * (1/5)</gadget>
<output>100</output>

<result>100</result>