Researchers are interested in estimating the mean change in student scores on their second attempt at the GRE Quantitative exam. History indicates the change in score is normally distributed with a...

Researchers are interested in estimating the mean change in student scores on their second attempt at the GRE Quantitative exam. History indicates the change in score is normally distributed with a standard deviation of 50. How large a sample should the researchers take they want to be with in 2 units of the true value with 95% confidence.