Maomao Bookstore held an event, and all books were 10% off. Mom bought the books for 108 yuan, which was much cheaper than the original price.
毛毛书店搞活动，所有书一律九折，妈妈买书共用了108元，比原价便宜了多少元．
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">108 / (9/10)</gadget>
<output>120</output>

<gadget id="calculator">120 - 108</gadget>
<output>12</output>

<result>12</result>