A researcher is interested in finding a 90% confidence interval for the mean number minutes students are concentrating on their professor during a one hour statistics lecture. The study included 126 students who averaged 35.3 minutes concentrating on their professor during the hour lecture. The standard deviation was 12.2 minutes. Round answers to 3 decimal places where possible.

a. To compute the confidence interval use a ? z or t distribution.

b. With90% confidence the population mean minutes of concentration is between______ and ______ minutes.

c.If many groups of 126 randomly selected members are studied, then a different confidence interval would be produced from each group. About____________ percent of these confidence intervals will contain the true population mean minutes of concentration and about____________ percent will not contain the true population mean minutes of concentration.