The original price of a storybook is 18 yuan, and it is sold at a 25% discount, which is much cheaper than the original price.
一本故事书原价18元，打七五折出售，比原价便宜了多少元．
<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">18 * (1/4)</gadget>
<output>9/2 = around 4.5</output>

<result>9/2 = around 4.5</result>