A book, Xiao Ming read it (1/7) on the first day and (4/7) on the second day, what percentage of the book is left unread?
一本书，小明第一天看了它的(1/7)，第二天看了它的(4/7)，还剩下这本书的几分之几没有看？
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">1 - (1/7) - (4/7)</gadget>
<output>2/7 = around 0.285714</output>

<result>2/7 = around 0.285714</result>