The school bought 280 new books, distributed 10 books to the teachers, and distributed the rest to 9 classes on average. How many books are distributed to each class on average?
学校买来280本新书，发给老师10本后，剩下的平均分给9个班，平均每班分多少本？
<gadget id="calculator">280 - 10</gadget>
<output>270</output>

<gadget id="calculator">270 / 9</gadget>
<output>30</output>

<result>30</result>