The selling price of a book is 26 yuan. After the book is sold, a 30% profit can be obtained. What is the cost of the book?
一本书的售价是26元，这本书售出后可获得30%的利润，这本书的成本是多少．
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 + (3/10)</gadget>
<output>13/10 = around 1.3</output>

<gadget id="calculator">26 / (13/10)</gadget>
<output>20</output>

<result>20</result>