prep

106.   11122-!-item-!-187;#058&007588

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

答案是A.这种题怎么做,每次看到都晕