The original price of a book is 20 yuan, and now it is sold at a 20% discount. How much is it selling now?
一本图书原价20元，现在打八折出售，现在卖多少元．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">20 * (4/5)</gadget>
<output>16</output>

<result>16</result>