做PREP遇到一道看不懂的PS题，有没有人可以解释一下？

Silense · 发表于 2011-10-30 17:40:11

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 standard deviation of the 10 running times is 22.4 seconds, rounded to the nearest tenth of a second, how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times?

(A) One
(B) Two
(C) Three
(D) Four
(E) Five

【答案】B

how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times? 这句话怎么理解？
1 standard deviation是什么意思？
整个题求的是什么概念？
（我本科是学语言专业的，已经好久没学数学了，希望大家可以帮帮忙）

deoxysjjy · 发表于 2011-10-30 18:25:57

同问，我也不明白

Lancer911 · 发表于 2011-10-30 18:38:50

算出mean是100，
那句话就是比mean少一个22.4
所以就是77.6以下就符合条件，所以是两个：70和75

anenxi · 发表于 2011-10-30 18:52:12

standard deviation，标准偏差，就是离平均的distance。这里已经说标准偏差是22.4.
how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times?
意思就是十个的平均远离22.4的有几个

Silense · 发表于 2011-10-30 20:11:20

同问，我也不明白

-- by 会员 deoxysjjy (2011/10/30 18:25:57)

看二楼的解释哟~

做PREP遇到一道看不懂的PS题，有没有人可以解释一下？

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