60 pears are divided into three classes, the first class is divided into 30, and the rest are equally divided into the second and third classes, how many are the second class.
60个梨分给三个班，一班分到30个，其余平均分给二、三班，二班分到多少个．
<gadget id="calculator">60 - 30</gadget>
<output>30</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<result>15</result>