Mr. Li reads a book, read this book in the first week (2/13), and read this book in the second week (7/13), and the rest of the book has not been read ?
李老师看一本书，第一周看了这本书的(2/13)，第二周看了这本书的(7/13)，还剩下这本书的几分之几没有看？
<gadget id="calculator">2 / 13</gadget>
<output>2/13 = around 0.153846</output>

<gadget id="calculator">7 / 13</gadget>
<output>7/13 = around 0.538462</output>

<gadget id="calculator">1 - (2/13) - (7/13)</gadget>
<output>4/13 = around 0.307692</output>

<result>4/13 = around 0.307692</result>