Market researches want to estimate the mean monthly expenditure on transport for households in Sydney. Randomly selected 40 households . The population standard deviation is 250. Sample mean is $350....

Market researches want to estimate the mean monthly expenditure on transport for households in Sydney. Randomly selected 40 households . The population standard deviation is 250. Sample mean is $350.

a) Calculate the lower limit and upper limit of 95% confidence interval?

b) If sample size is 10, can you still calculate the confidence interval with t or Z distribution? Reason