AMC8 2007

AMC8 2007 · Q7

AMC8 2007 · Q7. It mainly tests Linear equations, Averages (mean).

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?

房间里有5个人，平均年龄30岁。一个18岁的人离开了房间。剩下4人的平均年龄是多少？

(A) 25 25

(B) 26 26

(D) 33 33

(E) 36 36

Answer

Correct choice: (D)

正确答案：（D）

Solution

(D) Originally the sum of the ages of the people in the room is $5 \times 30 = 150$. After the 18-year-old leaves, the sum of the ages of the remaining people is $150 - 18 = 132$. So the average age of the four remaining people is $\frac{132}{4} = 33$ years.

（D）最初房间里所有人的年龄总和为 $5 \times 30 = 150$。18 岁的人离开后，剩下人的年龄总和为 $150 - 18 = 132$。因此，剩下四个人的平均年龄为 $\frac{132}{4} = 33$ 岁。

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