The arithmetic mean and standard deviation of a certain normal distribution are 15 and 1.5, respectively. What value is exactly 2 standard deviations less than the mean?
Choose the correct choice from the following answers:  A) 10.5  B) 11  C) 11.5  D) 12  E) 12.5

Rationale: the value which isexactlytwo sd less than the mean is : mean - 2 * sd = 15 - 2 * 1.5 = 12 . answer : d .
Answer: D