The average age of all the people in the classroom is 11 years old. If one teacher who is 30 years old is excluded and the average age of the rest is 10 years old, how many people are there in the classroom?
教室里所有人的平均年龄是11岁，如果不算其中1个30岁的老师，其余人的平均年龄是10岁，那么教室里有多少人？
<gadget id="calculator">30 - 10</gadget>
<output>20</output>

<gadget id="calculator">11 - 10</gadget>
<output>1</output>

<gadget id="calculator">20 / 1</gadget>
<output>20</output>

<result>20</result>