If you buy a book with a 20% discount and a 10% discount, it costs you 2 yuan less. What is the original price of the book?
购买一本书，打八折比打九折少花2元，则这本书原价是多少元
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(9/10) - (4/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">2 / (1/10)</gadget>
<output>20</output>

<result>20</result>