Question

To estimate the mean score μ of those who took the Medical College Admission Test on your campus, you will obtain the scores of an SRS of students. From published information, you know that the scores are approximately Normal with standard deviation about 6.6. How large an SRS must you take to reduce the standard deviation of the sample mean score to 1? (Round your answer up to the next whole number.)

Answer 1

Standard deviation for mean of n objects = (square root n) x s.d. for one 
object. 

So you need (2.8/0.5)^2 or around 32.