PP3 MATH

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

118.
                            12240-!-item-!-187;#058&008164 A

For a certain examination, a score of 58 was 2 standard deviations below the mean, and a score of 98 was 3 standard deviations above the mean.  What was the mean score for the examination?

(A) 74

(B) 76

(C) 78

(D) 80

(E) 82

这种题目我都不知道怎么做.虽然知道相关公式.

请问大家怎么做