1952 AMC 12 第 2 题

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

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

总平均成绩为

\dfrac{20(80)+30(70)}{50}

The combined average is

\dfrac{20(80)+30(70)}{50}

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.

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