Suppose that for budget planning purposes the city in Exercise 39 needs a better estimate of the mean daily income from parking fees.
(a) Someone suggests that the city use its data to create a 95% confidence interval instead of the 90% interval first created. Would this interval be better for the city planners? (You need not actually create the new interval.)
(b) How would the 95% interval be worse for the city planners?
(c) How could city planners achieve an interval estimate that would better serve their planning needs?
(d) How many days’ worth of data must planners collect to have 95% confidence of estimating the true mean to within $10? Does this seem like a reasonable objective? (Use a z-interval to simplify the calculations.)