Question

Garcia 老师询问健康课学生上周有多少天至少锻炼了三十分钟。

结果总结在下面的条形图中，柱子的高度表示学生人数。Garcia 老师班上学生报告的上周锻炼天数的平均数是多少？答案四舍五入到最接近的百分之一。

Mr. Garcia asked the members of his health class how many days last week they exercised for at least 30 minutes. The results are summarized in the following bar graph, where the heights of the bars represent the number of students.

What was the mean number of days of exercise last week, rounded to the nearest hundredth, reported by the students in Mr. Garcia's class?

$3.50$

$3.57$

$4.36$

$4.50$

$5.00$

答案：C

知识点：平均数数据与图表解读

难度评级：960

视频讲解：

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文字解答：

数出每种情况可知，锻炼 $1,2,3,4,5,6,7$ 天的有一人，锻炼 $1,3,2,6,8,3,2$ 天的有三人，锻炼 $25$ 天的有二人，锻炼天的有六人，锻炼天的有八人，锻炼天的有三人，锻炼天的有二人。

学生总数为 $\begin{aligned} &1\cdot1+2\cdot3+3\cdot2+4\cdot6\\ &\qquad+5\cdot8+6\cdot3+7\cdot2=109. \end{aligned}$

因此，锻炼天数总和为 $109/25=4.36$

平均锻炼天数等于总锻炼天数除以学生总数：所以正确答案是 C。

The bar heights for $1,2,3,4,5,6,7$ days are $1,3,2,6,8,3,2$ , for a total of $25$ students.

The total number of reported exercise days is $\begin{aligned} &1\cdot1+2\cdot3+3\cdot2+4\cdot6\\ &\qquad+5\cdot8+6\cdot3+7\cdot2=109. \end{aligned}$

The mean is $109/25=4.36$ days.

Thus, C is the correct answer.

2018 AMC 8 第 8 题

答案：C

难度评级：960

视频讲解：

文字解答：

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