A certain library purchased a batch of books, among which science and technology books accounted for 20%, literature and art books accounted for 480, and the remaining 240 were story books. How many books are there in this batch?
某图书馆购进一批图书，其中科技书占20%，文艺书有480本，余下的240本是故事书，这批书共有多少本？
<gadget id="calculator">480 + 240</gadget>
<output>720</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">720 / (4/5)</gadget>
<output>900</output>

<result>900</result>