A batch of apples is sold at 20% off, how much cheaper than the original
一批苹果按8折出售，比原来便宜多少
<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>

<result>1/5 = around 0.2</result>