find the differences between the mean and each of the n numbers ;
square each of the differences ;
find the average of the squared differences ;
take the nonnegative square root of this average.
Notice that the standard deviation depends on every data value, although it depends most on values that are farthest from the mean. This is why a distribution with data grouped closely around the mean will have a smaller standard deviation than data spread far from the mean.
GMAT数学的基本概念,其实没有想象中那么复杂和混乱。可以根据归类的GMAT数学基本概念词汇,加以复习和记忆。值得注意的是,GMAT数学的基本概念,最忌讳的是死记硬背,最好采用理解式记忆法,基本概念就能轻松搞定。
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