Question

You want to know how the commuting time of your employees compare to Departments competing for the same staff, so you get some survey data on average commuting times for 25 randomly selected people in your line of business.

Data: 59, 74, 73, 66, 80, 84, 90, 122.5, 37.2, 50, 139.3, 39, 80, 35, 88, 34, 82, 65, 61, 63, 66, 88, 70, 79, 75

You find that the mean commuting time is 72 minutes, with a standard deviation of 24.53. (Check for yourself!)

a) Calculate your standard error. (3 pts.)

b) Based on this, calculate a 95 percent Confidence Interval for the mean commuting time. (Remember, the C.I. is calculated by adding and subtracting from the observed sample mean the product of the standard error and the appropriate t-value; for the latter, you may use Excel tinv) Show your work. (7 pts.)

b) Given the data in the question above about mean commuting time, calculate the 90% Confidence Interval. (Again, show your work. (5 pts.)

c) Which is a bigger range, the 95% or 90% confidence interval? Why? (3 pts.)

d) What assumptions must you make about the population when constructing confidence interval estimates? (2 pts.)

Answer 1