A Random Sample of 25 Roundtrip Flights Between Philadelphia and Dallas

Multiple Choice

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