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[数学] Prep数学第34题编号2927-!-item-!-187;#058&003024

lzllfz问道:
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.

这题问什么不是c 方差的题我老错 都快疯了 方差的主要考点在哪里啊!!!


我的解答:
标准方差(Standard Deviation)主要考两个知识点:
1.标准方差的变化
关于标准方差的变化最重要是记住两条规则:
a)如果该数列中的每个数都同时增加或减少相同的数量,那么标准差不变。
b)如果该数列中的每个数都同时增加或减少相同的百分比,那么标准差对应增加或减少相同的百分比。
2.标准差与平均数的计算
假设平均数为m,标准差为d,那么考的最多的就是相比于m,差n个d如何计算。只需要算m±nd即可。

下面我说说这道题。

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