试读：

四、数据分析、统计和概率

Graphs, Statistics and Probability

1. Mean, Median and Mode

• Mean=average=sum/how many numbers

• Median: the middle value of a list

the average of the two middle values

To find the Median, place the numbers you are given in value order and find the middle number.

• Mode: the value or values that appear the greatest number of times (possible to have more than one)

• Weighted average: (x1f1+x2f2+… +xnfn)/(f1+f2+… +fn)

Example 38

7,8,2,3,9,4,6,5,10,6,6

Which of the following is true about the average(arithmetic mean), median, and mode of the 11 numbers

listed above?

A. The average, median, and mode are all different.

B. The average and median are the same, but the mode is different.

C. The average and mode are the same, but the median is different.

D. The median and mode are the same, but the average is different.

E. The average, median, and mode are all the same.

The answer is E.

Solution: 这题的关键点在于中位数，要先把数字按从大到小的顺序排列，得到2，3，4，5，6，6，

6，7，8，9，10. 所以这11 个数的中位数是6，众数也是6. 不难求出平均数也是6.

       ……

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