2007 AMC 8 第 7 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。
7.
一个房间里 个人的平均年龄是 岁。一名 岁的人离开房间。剩下四个人的平均年龄是多少？
The average age of people in a room is years. An -year-old person leaves the room. What is the average age of the four remaining people?
答案：D
小提示：
把原来的平均年龄转化为总年龄
Convert the original average into a total age.
大提示：
先减去离开者的年龄，再除以剩余人数
Subtract the age of the person who leaves before dividing by the remaining number of people.
解答：
起初，房间里所有人的总年龄为 岁。
这个人离开后，总年龄为 。剩下 人，平均年龄为 。
所以正确答案是 D。
Initially, the total age of everyone in the room is years.
After the person leaves, the total age is With people remaining, the average age becomes
Thus, D is the correct answer.
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