Posted by King on .
In a random sample of 1,000 exams, the average score was 500 points with a standard deviation of 80 points. Find the interval about the sample mean such that the probability is 0.90 that the mean number lies within the interval.

math 
PsyDAG,
90% = mean ± 1.645 SEm
SEm = SD/√n
I'll let you do the calculations.