Calculate a confidence interval for population mean assuming that each sample is form a normal population.
(1) sample mean = 30, population standard deviation = 28, number of sample n = 49 , 95 % confidence level
(2) sample mean = 10, population standard deviation = 9, number of sample n = 81, 99 % confidence level
Note that :
Confidence level 90% 95% 99%
Za/2 1.645 1.960 2.576