The selling price of a book after a 20% discount is 32 yuan, which is much cheaper than the original price.
一本书打八折后的售价是32元，比原价购买便宜了多少元．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">32 / (4/5)</gadget>
<output>40</output>

<gadget id="calculator">40 - 32</gadget>
<output>8</output>

<result>8</result>