Xinhua Bookstore shipped a batch of books, sold 45% of the books on the first day, and sold 35% of the books on the second day. It is known that 640 books were sold in two days. How many books in this batch?
新华书店运到一批图书，第一天卖出这批图书的45%，第二天卖出这批图书的35%，已知两天共卖出640本，这批图书共多少本？
<gadget id="calculator">45 / 100</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">35 / 100</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">(9/20) + (7/20)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">640 / (4/5)</gadget>
<output>800</output>

<result>800</result>