2. 外语
  3. A list has 100 numbers, the expectation of the list is 10 and the standard deviation of the list is 4, then which pair of the in

A list has 100 numbers, the expectation of the list is 10 and the standard deviation of the list is 4, then which pair of the in

admin2021-10-21  38
问题 A list has 100 numbers, the expectation of the list is 10 and the standard deviation of the list is 4, then which pair of the integers would make the standard deviation of the list decrease when the integers are put into the list?
选项 A、0, 20
B、0, 10
C、10, 10
D、-10, 0
E、-10, 10
答案C
解析 大家已经非常熟悉标准方差，现在把两个数加人数列中，那么求方差时公式中的分母n就变大了，如果分子能够保持不变的话，方差一定变小。现在expectation=10，期望也就是平均值等于10，而C中的两个数(10，10)减去平均值以后都为0，因此对分子没有任何贡献，分子保持不变，那么方差变小，所以选择C。
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