The original price of a basketball is 150 yuan, and now it is sold at a 20% discount, which is how much cheaper than the original price.
一个篮球原价150元，现在打八折出售，比原价便宜了多少元．
<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">150 * (1/5)</gadget>
<output>30</output>

<result>30</result>