Question

$33$ 名五年级学生的平均年龄为 $11$ 岁。他们的 $55$ 位家长的平均年龄为 $33$ 岁。所有这些家长和五年级学生的平均年龄是多少？

The average age of $33$ fifth-graders is $11.$ The average age of $55$ of their parents is $33.$ What is the average age of all of these parents and fifth-graders?

$22$

$23.25$

$24.75$

$26.25$

$28$

答案：C

知识点：平均数

难度评级：900

解答：

$33\cdot 11+55\cdot 33 = 66\cdot 33.$

总年龄为总人数为八十八，所以平均年龄为 $\dfrac{66\cdot 33}{88} = \dfrac 34 \cdot 33 = 24.75 .$

所以正确答案是 C。

The sum of the ages of all the fifth-graders and their parents is: $33\cdot 11+55\cdot 33 = 66\cdot 33.$

Then, as the average is the sum divided by the number of people, the average age must be: $\dfrac{66\cdot 33}{88} = \dfrac 34 \cdot 33 = 24.75 .$

Thus, the correct answer is C .

2013 AMC 10B 第 6 题

答案：C

难度评级：900

解答：

其他年份的第 6 题