Fangfang reads a book. She reads the whole book on the first day (3/13) and the whole book on the second day (4/13). How much of the book is left unread?
芳芳看一本书，第一天读了全书的(3/13)，第二天读了全书的(4/13)，这本书还剩下几分之几没有读？
<gadget id="calculator">3 / 13</gadget>
<output>3/13 = around 0.230769</output>

<gadget id="calculator">4 / 13</gadget>
<output>4/13 = around 0.307692</output>

<gadget id="calculator">1 - (3/13) - (4/13)</gadget>
<output>6/13 = around 0.461538</output>

<result>6/13 = around 0.461538</result>