A book, already read (3/7), how much of this book is left
一本书，已经看了(3/7)，还剩下这本书的多少
<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">1 - (3/7)</gadget>
<output>4/7 = around 0.571429</output>

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