Question

两个高中班级参加了同一场考试。一个班的 $20$ 名学生平均成绩为 $80\%$ ；另一个班的 $30$ 名学生平均成绩为 $70\%$ 。两个班全体学生的平均成绩为：

Two high school classes took the same test. One class of $20$ students made an average grade of $80\%$ ; the other class of $30$ students made an average grade of $70\%.$ The average grade for all students in both classes is:

$75\%$

$74\%$

$72\%$

$77\%$

以上答案均不正确

None of these

答案：B

知识点：加权平均数百分数

难度评级：1070

小提示：

按各班学生人数对该班平均成绩加权

Weight each class average by the number of students in that class

大提示：

总平均成绩为 $\dfrac{20(80)+30(70)}{50}$

The combined average is $\dfrac{20(80)+30(70)}{50}$

解答：

两个班的成绩总和为 $20(80)+30(70)=3700$ 个百分点，共有 $50$ 名学生。因此，总平均成绩为 $\frac{3700}{50}=74\%$ 。

因此，正确答案是 B。

The two classes earned a combined total of $20(80)+30(70)=3700$ percentage points among $50$ students. Their combined average is $\frac{3700}{50}=74\%.$

Thus, the correct answer is B.

1952 AMC 12 第 2 题

答案：B

难度评级：1070

小提示：

大提示：

解答：

其他年份的第 2 题