Xiaohong reads a story book. She reads 20 pages on the first day and 25% of the whole book on the second day. At this time, the ratio of those who have read to those who have not read is 9:11. How many pages does this storybook have?
小红看一本故事书，第一天看了20页，第二天看了全书的25%，这时已看的和没看的比是9：11．这本故事书共有多少页？
<gadget id="calculator">9 + 11</gadget>
<output>20</output>

<gadget id="calculator">9 / 20</gadget>
<output>9/20 = around 0.45</output>

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

<gadget id="calculator">(9/20) - (1/4)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">20 / (1/5)</gadget>
<output>100</output>

<result>100</result>