请教Prep PS2-166 标准方查题目

bipedalism

166.
                17879-!-item-!-187;#058&011634

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

请教各位朋友，最后一句没看懂，郁闷。。。。。。。。。。。。。

Rayakawr

B.

Mean=(90+105)/2=97.5

97.5-22.4=75.1

70 and 75 满足条件．

scarletohara

有点绕，不知道理解的是不是对的, 问有几个time离中数的距离大于一个标准方差？中数是100，所以只有75和70满足，选B

scarletohara

不好意思，是平均数，不是中数，但还是75 70满足

Rayakawr

Sorry, 没看仔细.是mean不是median.还是B?好巧,看样子今天运气不错.

哎,考试时真得当心...汗!

bipedalism

多谢多谢。这道题简直就是考阅读嘛，ft...