The original price of a storybook is 12.5 yuan, and the preferential price is 9.8 yuan, which is much cheaper than the original price.
一本故事书原价12.5元，优惠价是9.8元，比原价便宜了多少元．
<gadget id="calculator">12.5 - 9.8</gadget>
<output>2.7</output>

<result>2.7</result>