prep 数学请教！！

y0608x · 发表于 2010-2-9 15:11:30

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 schoolchildren to run a distance of 400 meters. If the starndard deviation of the 10 running times is 22.4 seconds, rounded to the nearest tenth of a second, how many of 10 running times are more than 1 starndard deviation below the mean of the 10 running times?
A.1 B.2 C.4 D.5 E.6
答案是B 我想问下这题什么意思？？

y0608x · 发表于 2010-2-9 22:45:27

大家帮帮忙~~ 后天要考试了...

tibet · 发表于 2010-2-9 23:06:37

你可真行
list都不给

y0608x · 发表于 2010-2-9 23:23:44

晕~ 怪不得没人理我
list 是70 75 80 85 90 105 105 130 130 130

tibet · 发表于 2010-2-9 23:32:34

求出平均值mean
mean减去1个standard deviation
比那个值小的数据个数就是了

y0608x · 发表于 2010-2-9 23:36:03

原来是这个意思~~ 感谢感谢~~~

prep 数学请教！！

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