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一道prep数学题，求解答~~
if a certain sample of data has a mean of 20.0 and a standard deviation of 3.0, which of the following values is more than 2.5 standard deviations from the mean?
a,12.0
b,13.5
c,17.0
d,23.5
e,26.5
这题没看懂，是什么意思？ |
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