There are 400 science and technology books in the school library, accounting for 20% of the total, and story books account for 30% of the total. How many story books are there?
学校图书室有科技书400本，占总数的20%，故事书占总数的30%，故事书有多少本？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">400 / (1/5)</gadget>
<output>2_000</output>

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

<gadget id="calculator">2_000 * (3/10)</gadget>
<output>600</output>

<result>600</result>