Xiao Ming, when reading a book, the ratio of those who have read to those who have not read is 1:3. If you read another 84 pages, the remaining pages will just account for (2/5) of the whole book. How many pages are there in total?
小明，看一本书，已读的与未读的比是1：3，若再读84页，则剩下的页数刚好占全书的(2/5)，全书一共多少页．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 + 3</gadget>
<output>4</output>

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

<gadget id="calculator">1 - (2/5) - (1/4)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">84 / (7/20)</gadget>
<output>240</output>

<result>240</result>