Xiao Ming reads a story book and has read 40% of the book, leaving 120 pages unread. How many pages does this book have?
小明读一本故事书，已经读了全书的40%，还剩120页没读，这本书共有多少页？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">120 / (3/5)</gadget>
<output>200</output>

<result>200</result>