Unoccupied seats on flights cause airlines to lose revenue. Suppose a large airline wants to estimate its average number of unoccupied seats per flight over the past year. To accomplish this, the records of 225 flights are randomly selected, and the number of unoccupied seats is noted for each of the sampled flights. (The data are saved in the NOSHOW file.) Descriptive statistics for the data are displayed in the Minitab printout, Figure 6.8.

Estimate μ, the mean number of unoccupied seats per flight during the past year, using a 90% confidence interval.

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Figure 6.8 Minitab confidence interval for mean, Example 6.3 Variable N Mean StDev SE Mean NOSHOWS 225 11.596 4.103 0.274 90% CI (11.144, 12.047)