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gmat数学a sample of data has a mean of 54.0 and a standard dev

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gmat数学
a sample of data has a mean of 54.0 and a standard deviation of 7.5.which of the following values is more than 2 standard deviation from the mean
A;38.5
B;39.0
C;46.5
D;61.5
E;69
求详解
2 standard deviation equals to 15(7.5 x 2=15.0)
then the 2-standard-deviation range should be 39(54-15=39.0) to 69(54+15=69)
Only A. 38.5 is not within this range, thus it's the correct answer for "more than 2 standard deviation"