Enjoy learning Statistics Online! Please be sure to share and subscribe to our YouTube channel.

30. The following Minitab display was created from speed data collected on a strip of I-95 where the
speed limit is posted as 55mph. Use the Minitab display below to identify the point estimate for
the population mean, and interpret the 95% confidence interval provided by Minitab.

I am not sure how this went completely over my head and i know the answer is in my face. can you shed some light on this please professor.

Posted to STATS 2 on Sunday, July 5, 2015   Replies: 1

Professor Mcguckian
07/05/2015
6:56 PM EST

Hi Miles,

The confidence interval given in the display is 66.655 to 68.114. The display says the sample mean is 67.3849. The point estimator for the population mean is the sample mean, so the point estimator is 67.3849.

Since the interval is from 66.655 miles per hour to 68.114 miles per hour, we can conclude with 95% confidence that the population mean is somewhere between these two speeds. Both of those speeds are greater than the posted speed limit of 55 mph, so we can safely conclude that the cars are speeding on average on this strip of road.