Science and technology books in the school library account for 40% of the total number of books, and story books account for 30% of the total number of books. There are 1,200 fewer story books than science and technology books. How many science and technology books are there?
学校图书馆科技书占图书总数的40%，故事书占图书总数的30%，故事书比科技书少1200本，科技书有多少本？
<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">1_200 / (1/10)</gadget>
<output>12_000</output>

<gadget id="calculator">12_000 * (2/5)</gadget>
<output>4_800</output>

<result>4_800</result>