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标题: [讨论]prep1-34 [打印本页]

作者: yifengjingyus 时间: 2007-8-25 07:39 标题: [讨论]prep1-34

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 gallon

作者: happypigfy 时间: 2007-8-25 18:48

选A，一个数列都加上同一个数，标准差没有影响。

条件（2）推不出

作者: yifengjingyus 时间: 2007-8-30 06:34

谢谢~~

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