Question

A survey of 77 commercial airline flights of under 2 hours resulted in a sample average late time for a flight of 2.42 minutes. The population standard deviation was 12 minutes. Construct a 95% confidence interval for the average time that a commercial flight of under 2 hours is late. What is the point estimate? What does the interval tell about whether the average flight is late? Appendix A Statistical Tables (Round your answers to 2 decimal places.) ≤ μ ≤ The point estimate is . The interval is . Since zero is in the interval, there is a possibility that, on average, the flights are .

Answer 1

Point estimate of mean = = 2.42

95% confidence interval is

X̅ ± Z( α /2) σ / √ ( n )
Z(α/2) = Z (0.05 /2) = 1.96
2.42 ± 1.96 * 12/√(77)
Lower Limit = 2.42 - 1.96 * 12/√(77)
Lower Limit = -0.2604
Upper Limit = 2.42 + 1.96 * 12/√(77)
Upper Limit = 5.1004

-0.26 < < 5.10

The interval is ( -0.26 , 5.10 )

Since zero is in the interval, there is a possibility that, on average, the flights are on time