A 20% discount for a book is 20 yuan, how much is the original price of this book.
一本书打八折是20元，这本书原价多少元．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">20 / (4/5)</gadget>
<output>25</output>

<result>25</result>