The original price of a book is 30 yuan, how much is the price after a 20% discount?
一本书原价30元，打八折后的价钱是多少元．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">30 * (4/5)</gadget>
<output>24</output>

<result>24</result>