From the three numbers A, B, and C, the number C is 2.5 times the average of A and B, and the sum of the numbers A and B is 15.2. What is the average of the three numbers A, B, and C?
由甲、乙、丙三个数，已经丙数是甲、乙的平均数的2.5倍，甲数与乙数的和是15.2，求甲、乙、丙三个数的平均数是多少？
<gadget id="calculator">15.2 / 2</gadget>
<output>7.6</output>

<gadget id="calculator">7.6 * 2.5</gadget>
<output>19</output>

<gadget id="calculator">19 + 15.2</gadget>
<output>34.2</output>

<gadget id="calculator">34.2 / 3</gadget>
<output>11.4</output>

<result>11.4</result>