The average of A and B is 2.6, the average of B and C is 2.8, the average of A and C is 2.1, find the average of A, B, and C.
甲、乙的平均是2.6，乙、丙的平均数是2.8，甲、丙的平均数是2.1，求甲、乙、丙三数的平均数．
<gadget id="calculator">2.6 * 2</gadget>
<output>5.2</output>

<gadget id="calculator">2.1 * 2</gadget>
<output>4.2</output>

<gadget id="calculator">2.8 * 2</gadget>
<output>5.6</output>

<gadget id="calculator">5.2 + 4.2 + 5.6</gadget>
<output>15</output>

<gadget id="calculator">15 / 2</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">(15/2) / 3</gadget>
<output>5/2 = around 2.5</output>

<result>5/2 = around 2.5</result>