The arithmetic mean and standard deviation of a certain normal distribution are 17.5 and 2.5, respectively. What value is exactly 2 standard deviations less than the mean?  Answers.
A) 10.5
B) 11
C) 11.5
D) 12
E) 12.5

Rationale: "mean = 17.5 two standard deviations is 2.5 + 2.5 = 5.0 there could be two calues for this . mean + two standard deviations = 22.5 mean - two standard deviations = 12.5 answer choice has 12.5 and so e is the answer ."
Answer: E