Part a) Since the variance of the underlying Normal distribution is not known, inference here would involve the t distribution. How many degrees of freedom would the relevant t distribution have?
Part b) Create a 95 % confidence interval for the mean speed of vehicles crossing the bridge. Give the upper and lower bounds to your interval, each to 2 decimal places. ( ,)
Part c) The police hypothesized that the mean speed of vehicles over the bridge would be the speed limit, 80 km/h. Taking a significance level of 5 %, what should infer about this hypothesis? A. We should reject the hypothesis since 80 km/h is in the interval found in (b). B. We should reject the hypothesis since the sample mean was not 80 km/h. C. We should not reject the hypothesis since the sample mean is in the interval found in (b). D. We should reject the hypothesis since 80 km/h is not in the interval found in (b). E. We should not reject the hypothesis since 80 km/h is in the interval found in (b).
Part d) Decreasing the significance level of the hypothesis test above would (select all that apply) A. decrease the Type I error probability. B. not change the Type I error probability. C. either increase or decrease the Type I error probability. D. not change the Type II error probability. E. increase the Type I error probability.
You can earn partial credit on this problem.