You wanted to estimate the mean number of vehicles crossing a busy bridge in your neighborhood each morning during rush hour for the past year (you wacky thing, you!). To accomplish this, you stationed yourself and a few assistants at one end of the bridge on 18 randomly selected mornings during the year and counted the number of vehicles crossing the bridge in a 10-minute period during rush hour. You found the mean to be 125 vehicles per minute with a standard deviation of 32.

(a) Calculate the 95% confidence interval for the population mean.

(b) State your conclusion from part (a) in words.

(c) Calculate the 99% confidence interval for the population mean.

(d) What do you notice about the difference between your answers for (a) and (c)? How do you explain this difference?