Find the 95% confidence interval for the difference in the mean costs of parking tickets in these two cities.
A)19.57 ± 20.00
B)19.57 ± 20.38
C)19.57 ± 18.98
D)19.57 ± 17.68

Question

Quizplus · Accepted Answer

Since the standard deviation of both samples is unknown, we will assume that they are not equal and use a t-distribution. 
Using a t-interval calculator with the given information, we get a 95% confidence interval of ( -0.81, 39.95) for the difference in mean costs of parking tickets between the two cities. 
Thus, the closest option is B, which has a range of 20.38, but the center of the range is slightly off from the actual confidence interval.

Find the 95% Confidence Interval for the Difference in the Mean