The school bought a batch of books, of which literature and art books accounted for (4/9), and mathematics books accounted for the rest (18/25). It is known that mathematics books are 20 fewer than literature and art books. How many books are there in total?
学校买来一批图书，其中文艺书占(4/9)，数学书占余下的(18/25)，已知数学书比文艺书少20本．这批图书共有多少本？
<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">1 - (4/9)</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">18 / 25</gadget>
<output>18/25 = around 0.72</output>

<gadget id="calculator">(5/9) * (18/25)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(4/9) - (2/5)</gadget>
<output>2/45 = around 0.044444</output>

<gadget id="calculator">20 / (2/45)</gadget>
<output>450</output>

<result>450</result>