Data Sufficient

The members of the newest recruiting class of a certain military organization are taking their physical conditioning test.and those who score in the bottome 16% will have to retest.If the scores are normally distributed,and have an arithmetic mean of 72, what is the score at or below which the recruits will have to retest?

1.there are 500 recruits in the class.

2.10 recruits scored 82 or higher.

答案选C。

我不是很明白the score ar normally distributed是什么意思啊？

看不明白答案解释说82与72之间有两个标准差。。。