Xiaoli reads a book. She reads 10% of the whole book on the first day, 25% of the whole book on the second day, and 30 pages on the third day, exactly half of the whole book. How many pages does this book have?
小丽读一本书，第一天读了全书的10%，第二天读了全书的25%，第三天读了30页，正好读了全书的一半，这本书共有多少页？
<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/2) - (1/10) - (1/4)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">30 / (3/20)</gadget>
<output>200</output>

<result>200</result>