There are 520 books in the school library that are not story books, and 500 books that are not science books. There are 600 books of known stories and science books. How many other books are there in the library?
学校图书室有520本书不是故事书，有500本不是科技书，已知故事和科技书共有600本，那么图书室其它书有多少本？
<gadget id="calculator">500 - 600</gadget>
<output>-100</output>

<gadget id="calculator">520 + (-100)</gadget>
<output>420</output>

<gadget id="calculator">420 / 2</gadget>
<output>210</output>

<result>210</result>