A 20% discount on a commodity, which used to cost 90 yuan, can now be reduced by a few yuan.
一种商品打八折，原来要90元，现在可以少用多少元．
<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">90 * (1/5)</gadget>
<output>18</output>

<result>18</result>