Dajun reads a book, reads 20% of the whole book on the first day, and reads 77 pages on the second day. At this time, the ratio of the number of pages read to unread is 3:5. How many pages does the book have?
大军读一本书，第一天读了全书的20%，第二天读了77页，这时已读的和未读的页数比是3：5．全书有多少页？
<gadget id="calculator">3 + 5</gadget>
<output>8</output>

<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

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

<gadget id="calculator">(3/8) - (1/5)</gadget>
<output>7/40 = around 0.175</output>

<gadget id="calculator">77 / (7/40)</gadget>
<output>440</output>

<result>440</result>