A new batch of books has just been displayed on a shelf in a bookstore. 60% of the books were sold on Saturday, and the remaining 65% were sold on Sunday. At this time, there were 231 books left on the shelf. How many books are there in this batch of new books?
书店里某书架上刚陈列出一批新图书．星期六卖出这批图书的60%，星期天卖出剩下的65%，这时书架上还剩下图书231本．这一批新图书有多少本．
<gadget id="calculator">65 / 100</gadget>
<output>13/20 = around 0.65</output>

<gadget id="calculator">1 - (13/20)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">60 / 100</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">231 / (7/20) / (2/5)</gadget>
<output>1_650</output>

<result>1_650</result>