Xiaohong reads a book. She reads (1/7) of the whole book on the first day and (2/7) of the whole book on the second day. What percentage of the book is left?
小红看一本书，第一天看了全书的(1/7)，第二天看了全书的(2/7)，还剩几分之几没有看？
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 - (1/7) - (2/7)</gadget>
<output>4/7 = around 0.571429</output>

<result>4/7 = around 0.571429</result>