A book has been read (3/5), and there are still 20 pages left, how many pages does this book have? What is the column
一本书，已看了(3/5)，还剩下20页没有看，求这本书有多少页？列式为多少
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">20 / (2/5)</gadget>
<output>50</output>

<result>50</result>