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标题: 还有一题prep 晕？ [打印本页]

作者: stormyyu 时间: 2007-12-19 22:33
标题: 还有一题prep 晕？

the residents of town x participated in a survey to determine the number of hours per week each resident spend watching tv,the distribution of the results of the survey had a mean of 21 hours and a stand deviation of 6 hours.the number of hours the pat, a resident of town x, watched tv last week was between 1 and 2 standard deviations below the mean. which of the following could be the number of hours that pat watched tv last week?

30 , 20, 18, 12, 6

作者: mych666666 时间: 2007-12-20 00:47

是12吗？一倍Std.范围是15(21-6)，两倍是9，在1，2倍之间，应该是在9到15之间吧。

作者: stormyyu 时间: 2007-12-20 02:31

是12

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