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标题: PREP一道数学关于标准差 在线等 [打印本页]

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作者: sunjin1988    时间: 2009-10-18 22:02
标题: PREP一道数学关于标准差 在线等

70, 75, 80, 85, 90, 105, 105, 130,130,130

The list shown consists of the times, in seconds, that it took each of 10 students to run a distance of 400 meters. If the std. deviation of the 10 running times is 22.4 sec, rounded to nearest tenth of a second , how many of the 10 running times are more than 1 Std deviation below the mean of the 10 running times?

1) One
2) two
3)three
4) four
5)five

Answer is : 2

 
这个题目怎么回事 我不太懂 请牛人解释下 这个more than 1 standard deviation 怎么理解

[此贴子已经被作者于2009/10/18 22:04:01编辑过]

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作者: frankmfg    时间: 2009-10-18 22:30
mean: 100
One standard deviation below mean would be values of 70 and 75

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作者: biglin1987    时间: 2009-10-18 22:35
 more than 1 Std deviation below the mean of the 10 running times就是比平均数低一个标准差还多的数，平均数是100，标准差是22.4，就是问比100-22.4小的有几个。有70, 75。所以答案是2.

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作者: sunjin1988    时间: 2009-10-18 22:49

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