There are 8,400 books in the school library, among which science and technology books account for all (3/8), literature and art books account for all (4/21), and the rest are children's books. How many children's books are there?
学校图书室有8400本图书，其中科技书占全部的(3/8)，文艺书占全部的(4/21)，其余是儿童读物，儿童读物多少本？
<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">4 / 21</gadget>
<output>4/21 = around 0.190476</output>

<gadget id="calculator">1 - (3/8) - (4/21)</gadget>
<output>73/168 = around 0.434524</output>

<gadget id="calculator">8_400 * (73/168)</gadget>
<output>3_650</output>

<result>3_650</result>