There are four numbers A, B, C and D, the average of the two numbers A and B is 81, the average of the two numbers B and C is 89.5, the average of the two numbers C and D is 92, A, The average of the two numbers D is 83.5, find the average of the four numbers A, B, C, D.
有A，B，C，D四个数，A，B两个数的平均数为81，B，C两个数的平均数为89.5，C，D两个数的平均数为92，A，D两个数的平均数为83.5，求A，B，C，D四个数的平均数．
<gadget id="calculator">81 + 89.5 + 92 + 83.5</gadget>
<output>346</output>

<gadget id="calculator">2 / 2 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">346 * (1/4)</gadget>
<output>173/2 = around 86.5</output>

<result>173/2 = around 86.5</result>