Question

一个房间里 $5$ 个人的平均年龄是 $30$ 岁。一名 $18$ 岁的人离开房间。剩下四个人的平均年龄是多少？

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?

$25$

$26$

$29$

$33$

$36$

答案：D

知识点：平均数

难度评级：900

解答：

起初，房间里所有人的总年龄为 $5 \cdot 30 = 150$ 岁。

这个人离开后，总年龄为 $150 - 18 = 132$ 。剩下 $4$ 人，平均年龄为 $\dfrac{132}{4} = 33$ 。

所以正确答案是 D。

Initially, the total age of everyone in the room is $5 \cdot 30 = 150$ years.

After the person leaves, the total age is $150 - 18 = 132.$ With $4$ people remaining, the average age becomes $\dfrac{132}{4} = 33.$

Thus, D is the correct answer.

2007 AMC 8 第 7 题

答案：D

难度评级：900

解答：

其他年份的第 7 题