Li read a book, read (1/4) of the whole book on the first day, (1/3) of the whole book on the second day, read 20 pages on the third day, and left 30 pages unread, this book How many pages are there?
李看一本书，第一天看了全书的(1/4)，第二天看了全书的(1/3)，第三天看了20页，还剩30页没看，这本书共有多少页？
<gadget id="calculator">20 + 30</gadget>
<output>50</output>

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

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

<gadget id="calculator">1 - (1/4) - (1/3)</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">50 / (5/12)</gadget>
<output>120</output>

<result>120</result>