If you buy a book with a 20% discount, you can save it by 3 yuan. How much should you pay if you buy it at the original price?
一本书打八折买可以便宜3元，按原价买应付多少元．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">3 / (1/5)</gadget>
<output>15</output>

<result>15</result>