Practice problem for module 2

A random sample of 50 students GPA reveals that the mean GPA is 2.8 years with a standard deviation of 0.45 years. (a) Construct a 95% Confidence Interval for the mean lifetime of all LED TV.

(b) If we want to be 90% confident, and we want to control the maximum error of estimation to be 0.2, how many more students should be added into the given sample?

(c) Would you conclude that the mean GPA more than 2.5 at 5% level of significance?