题目
Consider the following 20 items listed in ascending order:「huixue_img/importSubject/1564548695985360896.png」The median value of the items is closest to:
选项
A.4.
B.5.
C.3.
答案
A
解析
The median is the value of the middle item of a set of items that has been sorted into ascending or descending order. In an even-numbered sample, we define the median as the mean of the values of items occupying the n/2 and (n +2)/2 positions (the two middle items). The n/2 item is the 10th item and the (n +2)/2 item is the 11th item. The value of the 10th item is 3; the value of the 11th item is 5. The mean of 3 and 5 is 4. 中位数是按升序或降序排序的一组项的中间项的值。在偶数样本中，我们将中位数定义为占据n/2和（n＋2）/2位置（中间两个项目）的项目值的平均值。在题干中，n/2项是第10项，（n＋2）/2项是第11项。 因为第10项的值是3；第11项的值是5。 3和5的平均数是(3＋5）/2=4。