The four numbers A, B, C, and D can be paired to form six pairs. The averages of these six logarithms are 12, 13, 15, 17, 19, and 20, respectively. Please think about how to match, and find the average of the original four numbers.
A、B、C、D四个数，两两配对可以成六对．这六对数的平均数分别是12，13，15，17，19，20．请你先想一想，是怎样配对的，并求原来四个数的平均数．
<gadget id="calculator">12 + 13 + 15 + 17 + 19 + 20</gadget>
<output>96</output>

<gadget id="calculator">2 / 3 / 4</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">96 * (1/6)</gadget>
<output>16</output>

<result>16</result>