A personnel manager has found that historically the scores on aptitude tests given to applicants for entry level positions follow a normal distribution with a standard deviation of 32.4 points. A random sample of nine test scores from the current group of applicants had a mean score of 187.9 points.

c) What sample size should be used to if we want to have Margin of Error less than 50?

d) Without doing calculation, what change do we observe if standard deviation increases to 150 test scores? Explain your answer.

e) Without doing calculation, what change do we observe if confidence level increases to 90% scores? Explain your answer.

f) Is it reliable to use point estimator to predict the value of unknown population parameter in this context?