There are five numbers whose average is 60. If these five numbers are arranged in descending order, then the average of the first three numbers is 70, and the average of the last three numbers is 50. What is the number in the middle?
有五个数它们的平均数是60．如果把这五个数按从大到小的顺序排列，那么前三个数的平均数是70，后三个数的平均数是50．求中间这个数是多少？
<gadget id="calculator">70 * 3</gadget>
<output>210</output>

<gadget id="calculator">50 * 3</gadget>
<output>150</output>

<gadget id="calculator">60 * 5</gadget>
<output>300</output>

<gadget id="calculator">150 - 300</gadget>
<output>-150</output>

<gadget id="calculator">210 + (-150)</gadget>
<output>60</output>

<result>60</result>