The average of the numbers A, B, and C is 12, and their ratio is (1/2): (2/3): (5/6). What is the number of C?
甲、乙、丙三数的平均数为12，它们的比是(1/2)：(2/3)：(5/6)，丙数是多少．
<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">12 * 3 * (5/12)</gadget>
<output>15</output>

<result>15</result>