9. 10个小孩跑步, 共跑400米. 所花的时间以秒计分别为 70 75 80 85 90 105 105 130 130 130. 标准差为22.4. 问How many children are more than one 方差below the average? 答案有一个, 两个, 三个, 四个 和五个. 我选了两个, 不知是否理解有错误. 所以把问题的原句写出来供参考.
i agree , two
I don't calculate the mean , but estimate , it should be about 100
then one 'sigma' below the mean is about 78 then two kids run more than sigma below the ave
