2 standard deviation（sd）是2倍sd的意思吗,可以这样省略比较级?
A list of numbers has a mean of a standard deviation of 2.5.If x is a number in the list that is 2 standard deviations above the mean,what is the value of
这是新GRE官方指南上149页的一道题啊，不好意思，开头是...has a means of 8 and a standard deviation...