In a book, 1/3 of the total number has been read and there are 15 more pages. The ratio of the number of pages read to the number of unread pages is 2:3. How many pages are there in the book?
一本书，已读了总数的(1/3)还多15页，已读的页数与未读的页数比是2：3，全书共多少页．
<gadget id="calculator">2 + 3</gadget>
<output>5</output>

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

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(2/5) - (1/3)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">15 / (1/15)</gadget>
<output>225</output>

<result>225</result>