After reading a book in two days, I read 45% of the whole book on the first day, and read 40 pages less than the second day. How many pages is this book?
一本书两天看完，第一天看了全书的45%，比第二天少看40页，这本书多少页？
<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">(11/20) - (9/20)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">40 / (1/10)</gadget>
<output>400</output>

<result>400</result>