Xiaofang reads a science and technology book. She reads 25% of the total pages of the book on the first day and 20% of the total pages of the book on the second day. She reads a total of 90 pages in two days. How many pages does this book have?
小芳看一本科技书，第一天看了全书总页数的25%，第二天看了全书总页数的20%，两天一共看了90页，这本书共有多少页？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/4) + (1/5)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">90 / (9/20)</gadget>
<output>200</output>

<result>200</result>