AMC 8 2007 Problem 7
AMC8 2007 年第 7 题
统计与数据图表★★☆☆☆
The average age of 5 people in a room is 30 years. An 18 -year-old person leaves the room. What is the average age of the four remaining people?
一个房间里 5 个人的平均年龄是 30 岁。一个 18 岁的人离开了这个房间。那么剩下的 4 人平均年龄是多少岁？
- A.25
- B.26
- C.29
- D.33
- E.36
正确答案 · Correct Answer
D
解析 · Solution
Solution 1
Let be the average of the remaining 4 people. The equation we get is Simplify, 4x + 18 = 1504x = 132x = 33 Therefore, the answer is 33
Since an 18 year old left from a group of people averaging 30, The remaining people must total 30 - 18 = 12 years older than 30. Therefore, the average is years over 30. Giving us 33
The total ages would be 30*5=150. Then, if one 18 year old leaves, we subtract 18 from 150 and get 132. Then, we divide 132 by 4 to get the new average, 33
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