My sister reads a book, and reads 15% of the whole book in the first week, and 25% of the whole book in the second week. Read 20 more pages in the second week than in the first week. How many pages does this book have?
姐姐看一本书，第一周看了全书的15%，第二周看了全书的25%．第二周比第一周多看20页．这本书一共有多少页？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(1/4) - (3/20)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">20 / (1/10)</gadget>
<output>200</output>

<result>200</result>