There are 310 books. After distributing them to 15 classes, there are still 10 books left. How many books are divided into each class on average.
有310本书，分给15个班后，还剩下10本，平均每个班分多少本．
<gadget id="calculator">310 - 10</gadget>
<output>300</output>

<gadget id="calculator">300 / 15</gadget>
<output>20</output>

<result>20</result>