Twelve different video games showing substance use were observed and the duration of times of game play? (in seconds) are listed below. The design of the study justifies the assumption that the sample can be treated as a simple random sample. Use the sample data to construct an 80% confidence interval estimate of sigma?, the standard deviation of the duration times of game play. Assume that this sample was obtained from a population with a normal distribution.
4,247
3,925
4,706
4,044
3,927
4,423
3,924
4,673
4,656
3,857
4,527
4,524
The confidence interval estimate is