The age distribution of students in a class is as follows: 3 students are 13 years old, 15 are 12 years old, 11 are 11 years old, and 21 are 10 years old. What is the average age of the students in this class?
某班的学生的年龄分布情况如下：13岁有3人，12岁有15人，11岁有11人，10岁的有21人．这个班同学的平均年龄是多少岁．
<gadget id="calculator">13 * 3</gadget>
<output>39</output>

<gadget id="calculator">12 * 15</gadget>
<output>180</output>

<gadget id="calculator">11 * 11</gadget>
<output>121</output>

<gadget id="calculator">10 * 21</gadget>
<output>210</output>

<gadget id="calculator">39 + 180 + 121 + 210</gadget>
<output>550</output>

<gadget id="calculator">3 + 15 + 11 + 21</gadget>
<output>50</output>

<gadget id="calculator">550 / 50</gadget>
<output>11</output>

<result>11</result>