The average of five numbers is 12.48, the average of the first three numbers is 10.6, and the average of the last three numbers is 16.4. What is the middle number?
有五个数的平均数是12.48，前三个数的平均数是10.6，后三个数的平均数是16.4，中间一个数是多少．
<gadget id="calculator">10.6 * 3</gadget>
<output>31.8</output>

<gadget id="calculator">16.4 * 3</gadget>
<output>49.2</output>

<gadget id="calculator">31.8 + 49.2</gadget>
<output>81</output>

<gadget id="calculator">12.48 * 5</gadget>
<output>62.4</output>

<gadget id="calculator">81 - 62.4</gadget>
<output>18.6</output>

<result>18.6</result>