Quiz 08 Chapter 9 Section 2 • Name:


1. This afternoon, 04 November 2005 at 4:00 P.M., the college will hold a 10.329 km fun walk/run from the campus to Spanish Wall. The college has not done this walk in many years, not since the late 1990s. The duration in hours of ten randomly selected students was recorded during the last walk. Use the data to determine the sample mean x and the sample standard deviation sx. Use the n, x, and sx to calculate a 95% confidence interval c for the population mean walk duration.

  1. sample size: n = ______________
  2. sample mean: x = ______________
  3. sample standard deviation: sx = ______________
  4. confidence level: c = ______________
  5. degrees of freedom: df = ______________
  6. t-critical: tc = ______________
  7. Error tolerance E: = ______________
  8. Calculate the confidence interval for the population mean arrival time:

    P( ___________ ≤ ≤ ___________ ) = 0.95
  9. Optional homework: If you walk this afternoon, keep track of how long it takes you to walk to Spanish wall. Report your time to me this evening at Spanish wall or email me your time as an optional homework.
Confidence interval statistics
Degrees of freedom df = n-1 =COUNT(data)-1
Find a tc value from a confidence level c and sample size n tc   =TINV(1-c,n-1)
Calculate an error tolerance E of a mean for any n ≥ 5 using sx. E error_tolerance_tc.gif (989 bytes) =tc*sx/SQRT(n)
Calculate a confidence interval for a population mean from a sample mean x and an error tolerance E   x-E≤  ≤ x+E  

For those who like to work with a sketch: normal curve