The school bought 580 books, and after distributing them to 24 classes, there were still 100 books left. How many copies are distributed to each class on average?
学校买来580本书，发给24个班后还剩100本．平均发给每个班多少本？
<gadget id="calculator">580 - 100</gadget>
<output>480</output>

<gadget id="calculator">480 / 24</gadget>
<output>20</output>

<result>20</result>