Obviously read a book and read part of it in the morning. At this time, the number of pages read is 1/9 of the number of unread pages. If you read 7 pages more in the afternoon than in the morning, the ratio of the number of pages you have read to the number of unread pages is It is 11:9, how many pages does this book have?
明明读一本书，上午读一部分，这时已读的页数是未读页数的(1/9)，下午比上午多读7页，这时已读页数与未读页数的比是11：9，这本书共有多少页？
<gadget id="calculator">11 + 9</gadget>
<output>20</output>

<gadget id="calculator">11 / 20</gadget>
<output>11/20 = around 0.55</output>

<gadget id="calculator">1 + 9</gadget>
<output>10</output>

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

<gadget id="calculator">(1/10) * 2</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(11/20) - (1/5)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">7 / (7/20)</gadget>
<output>20</output>

<result>20</result>