PREP上的一道ps数学题，希望大家看看，帮助我！！！！感谢！

zf13646348

求助！！拜托大家给点提示，题我也读不懂更不会做！希望高手帮助翻译下，在解析一下！！Many thanks！

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 metres. If the standard deviation of the 10 running times is 24.4 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?
A1 B2 C3 D4 E5  ·
求大家帮助我一下~感谢！！！

alohawilliam

B?

zf13646348

恩，答案是B，请帮忙解释一下吧！！

sunhan915

算出这10个数的mean是100  然后 mean减去一个standard deviation  就是100-24.4 = 75.6  有两个比75.6小

zf13646348

感谢楼上！！