In a random sample of 26 people, the mean commute time to work was 34.6 minutes and the standard deviation was 7.2 minutes. Assume the population is normally distributed and use a t-distribution to construct a 80% confidence interval for the population mean u. What is the margin of error of u? Interpret the results. The confidence interval for the population mean u is (Round to one decimal place as needed.)

The distribution of study times for first-year students follow a Normal distribution with a standard deviation σ = 48 minutes. Suppose a sample of 344 students found that the mean study time for these students was x¯= 170 minutes per week. Use this to find a 94.38% confidence interval to estimate the mean study time for all students. We are 94.38% confident that the mean study time for first-year students is between the following ( answer) minutes and  ( answer) minutes. The answer needs to be the mean study time for first-year students is between what amount of minutes and the following minutes.

The standard deviation, S, for the annual medical cost of 24 households was found to equal $1689 find a 95% confidence interval for the standard deviation of the annual medical cost for all households. Assume medical costs are normally distributed.

In a recent sample of 89 used cars sales costs, the sample mean was $6,225 with a standard deviation of $3,151. Assume the underlying distribution is approximately normal.   Which distribution should you use for this problem? Construct a 95% confidence interval for the population mean cost of a used car.