There are 50 students in the class, 17 of them are 10 years old, 18 are 11 years old, and the rest are 9 years old. What is the average age of this class?
全班有50人，其中17人10岁，18人11岁，其余的全是9岁，求这个班的平均年龄是多少岁？
<gadget id="calculator">17 * 10</gadget>
<output>170</output>

<gadget id="calculator">18 * 11</gadget>
<output>198</output>

<gadget id="calculator">170 + 198</gadget>
<output>368</output>

<gadget id="calculator">50 - 17 - 18</gadget>
<output>15</output>

<gadget id="calculator">15 * 9</gadget>
<output>135</output>

<gadget id="calculator">368 + 135</gadget>
<output>503</output>

<gadget id="calculator">503 / 50</gadget>
<output>503/50 = around 10.06</output>

<result>503/50 = around 10.06</result>