The original price of 40 yuan is 25% off, which is equivalent to how much the price is reduced.
原价40元的商品打七五折，相当于降价多少元．
<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">40 * (1/4)</gadget>
<output>10</output>

<result>10</result>