Science and technology books in the school library account for 30% of the total number of books, and story books account for 50% of the total number of books. There are 600 fewer science and technology books than story books. How many books are there in the school library?
学校图书馆科技书占图书总数的30%，故事书占图书总数的50%，科技书比故事书少600本，学校图书馆共有图书多少本？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(2/5) - (3/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">600 / (1/10)</gadget>
<output>6_000</output>

<result>6_000</result>