There are three children, their average age is 12 years old, their age ratio is 3:4:5, what is the youngest age?
有三个小孩子，他们的平均年龄是12岁，他们年龄的比是3：4：5，最小的年龄是多少岁．
<gadget id="calculator">12 * 3</gadget>
<output>36</output>

<gadget id="calculator">3 + 4 + 5</gadget>
<output>12</output>

<gadget id="calculator">3 / 12</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">36 * (1/4)</gadget>
<output>9</output>

<result>9</result>