The number of pages read in a book is 1/4 of the number of unread pages. If you read another 220 pages, the number of unread pages is 1/3 of the number of pages read. How many pages are there in this book? ?
一本书已读的页数是未读页数的(1/4)，如果再读220页，那么未读的页数是已读页数的(1/3)，这本书共有多少页？
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 + 4</gadget>
<output>5</output>

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

<gadget id="calculator">(3/4) - (1/5)</gadget>
<output>11/20 = around 0.55</output>

<gadget id="calculator">220 / (11/20)</gadget>
<output>400</output>

<result>400</result>