请教一道PREP数学关于标准差的题~

mjrmjr0213

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? 答案 ONE TWO THREE FOUR FIVE  
请问答案是TWO 吗？ 100-22.4=77.6   因为没有这题的答案，希望以前做过的同学求证答案，谢谢

jsmart

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