There are three teachers, their average age is 40 years old, their age ratio is 3:4:5, what is the age of the youngest of the three teachers?
有三位老师，他们的平均年龄是40岁，他们年龄的比是3：4：5，这三个老师中年龄最小的是多少岁．
<gadget id="calculator">40 * 3</gadget>
<output>120</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">120 * (1/4)</gadget>
<output>30</output>

<result>30</result>