请教一道标准方法问题 多谢

msufcufou

34.
During an experiment, some water was removed from each of 6 water tanks.  If the standard deviation of the volumes of water in the tanks at the beginning of the experiment was 10 gallons, what was the standard deviation of the volumes of water in the tanks at the end of the experiment?
(1) For each tank, 30 percent of the volume of water that was in the tank at the beginning of the experiment was removed during the experiment.
(2) The average (arithmetic mean) volume of water in the tanks at the end of the experiment was 63 gallons.

答案 a

lenghongmin

这道题讲的就是方差 要理解方差的意思 就是表示一堆数的离散程度 这道题A说6桶水每桶都remove掉了30% 这样一来并没有影响着6桶水原来的离散程度 所以还是10gallon
个人理解 不对的话大家指正

lilingfeng

我觉得选e，每个水桶都remove掉了30%，但是他们remove掉的量是不同的，会影响离散程

度。简单的例子：
假设2个水桶分别有4,6，假设remove掉了50%
那么标准差由原来的1变成了0。5
所以我觉得选e

ps：每个桶减少一样的量时，标准差不变

lenghongmin

恩 对的对的 有道理 我想当然了 这种题目应该举举例子的