For a book, Xiao Ming has read 40% of it, and the remaining part is 20 pages more than the part he has read. How many pages does this book have?
一本书，小明已经看了它的40%，剩下的部分比已经看的部分多20页，这本书有多少页？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5) - (2/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">20 / (1/5)</gadget>
<output>100</output>

<result>100</result>