A random sample of 25 roundtrip flights between Philadelphia and Dallas has an average airfare of $393.50 with a sample standard deviation of $50.30. The critical value for an 80% confidence interval around this sample mean is ------.
A)1.318
B)0.857
C)1.711
D)2.064

Question

Quizplus · Accepted Answer

The critical value for an 80% confidence interval can be found using a t-distribution table or calculator because the population standard deviation is unknown and the sample size is relatively small (n=25). For an 80% confidence level and a sample size of 25, the degrees of freedom (df) would be 24 (n-1). Looking up the critical value for 80% confidence and 24 df in a t-distribution table gives us a value close to 1.318.

A Random Sample of 25 Roundtrip Flights Between Philadelphia and Dallas