A new batch of children's books arrived at Xinhua Bookstore. They sold 3/8 of the total on the first day, and 40% of the total on the second day. There are still 450 books left. How many children's books are there in this batch?
新华书店新到一批儿童读物，第一天卖出总数的(3/8)，第二天卖出总数的40%，还余下450本，这一批儿童读物一共有多少本？
<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (3/8) - (2/5)</gadget>
<output>9/40 = around 0.225</output>

<gadget id="calculator">450 / (9/40)</gadget>
<output>2_000</output>

<result>2_000</result>