When reading a book, I read (1/4) of the whole book on the first day, and read 120 pages on the second day. At this time, the ratio of the number of pages read to the number of unread pages is 2:3. How many pages does this book have?
看一本书，第一天看了全书的(1/4)，第二天看了120页，这时已读与未读页数的比是2：3，这本书有多少页？
<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

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

<gadget id="calculator">(2/5) - (1/4)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">120 / (3/20)</gadget>
<output>800</output>

<result>800</result>