## Elementary Statistics (12th Edition)

a) The sample size is large (at least 30), hence the ditribution is rougly normal. Standard deviation is unknown hence we will have to use t-distribution to estimate $\mu$. b)The sample size is large (at least 30), hence the ditribution is rougly normal. Standard deviation is known hence we will have to use z-distribution to estimate $\mu$. c) The distribution is not normal, hence we cannot estimate a confidence interval. d) The distribution is normal, hence we can use the chi-square distribution to estimate $\sigma$'s confidence interval.