The original price of a book is 20 yuan, and the price is now reduced by 25%. How much should I pay for this book?
一种书原价为20元，现在降价25%，现在买这本书应付多少钱？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">20 * (3/4)</gadget>
<output>15</output>

<result>15</result>