The ratio of the three numbers A, B and C is 3:4:5, and their average is 20, so what is the number C?
甲、乙丙三个数的比是3：4：5，它们的平均数是20，那么，丙数是多少．
<gadget id="calculator">20 * 3</gadget>
<output>60</output>

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

<gadget id="calculator">5 / 12</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">60 * (5/12)</gadget>
<output>25</output>

<result>25</result>