After a book is sold with a 20% discount, the current price is 40 yuan, how much is the original price?
一本书打八折出售后现价40元，原价多少元．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">40 / (4/5)</gadget>
<output>50</output>

<result>50</result>