Xiao Ming reads a story book, and reads 45% of the whole book in the first week, leaving 220 pages unread. How many pages does this book have.
小明看一本故事书，第一周看了全书的45%，还剩下220页没有看．这本书共有多少页．
<gadget id="calculator">45 / 100</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">1 - (9/20)</gadget>
<output>11/20 = around 0.55</output>

<gadget id="calculator">220 / (11/20)</gadget>
<output>400</output>

<result>400</result>