2004 AMC 8 第 9 题
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所有题目均经美国数学协会（MAA）官方合法授权使用。
9.
一个列表中五个数的平均数是 。前两个数的平均数是 。后三个数的平均数是多少？
The average of the five numbers in a list is The average of the first two numbers is What is the average of the last three numbers?
答案：D
小提示：
把每个平均数转化为总和
Turn each average into a sum.
大提示：
从五个数总和中减去前两个数的总和
Subtract the sum of the first two numbers from the sum of all five.
解答：
个数的总和是 。前 个数的总和是 。
后 个数的总和是 ，所以平均数是 。
所以正确答案是 D。
The sum of all numbers is The sum of the first numbers is
The sum of the last numbers is The average is therefore
Thus, D is the correct answer.
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