Statistics Confidence Intervals - Population Mean no Given

Question

The population standard deviation for the age of YZ College students is 15 years. If we want to be 95% confident that the sample mean age is within two years of the true population mean age of YZ College students, how many randomly selected YZ College students must be surveyed?

Answer 1

sample size = (z * S/ E)^2

z for 95% confident is 1.96

s is given as 15

E is given as 2

sample size = (1.96 * 16/2)^2 = 245/8624 ~ 2145