The average age of Nannan and Beibei is 11 years old, and the average age of Dongdong and Nannan is 15 years old, so how much younger is Beibei than Dongdong?
南南、北北两个人的平均年龄是11岁，东东、南南两个人的平均年龄是15岁，那么北北比东东小多少岁．
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">11 * 2</gadget>
<output>22</output>

<gadget id="calculator">30 - 22</gadget>
<output>8</output>

<result>8</result>