The students in the three classes of the sixth grade donated 500 books to Hope Primary School, the first class donated this batch of books (1/4), the second class donated these books (3/10), how many books did the third class donate ?
六年级三个班的同学向希望小学捐书500本，一班捐了这批书的(1/4)，二班捐了这批书的(3/10)，三班捐了多少本书？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (1/4) - (3/10)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">500 * (9/20)</gadget>
<output>225</output>

<result>225</result>