1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Calculate the confidence interval (Statistics problem)

  1. Jul 2, 2011 #1
    I am trying to calculate the confidence interval for this problem using my T-84, and it's driving me mad because I'm so close to the correct answer. The problem is

    1. The problem statement, all variables and given/known data


    The answer to this problem is (22769.83, 30059.41) (This is an example problem.) When I try to duplicate this in my calculator, my answer is (22772,30058).

    2. Relevant equations
    I go to STAT>TESTS>7>STATS

    3. The attempt at a solution

    I put the data in like this
    standard deviation: 8150
    mean: 26414.62
    n: 20
    C-Level: 0.9544

    Could someone tell me what I'm doing incorrectly, please.
  2. jcsd
  3. Jul 3, 2011 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I'm not familiar with your calculator but my guess is some problem with the Z values. If you check you will see that 95.44% corresponds to a right and left tail are each of .0228 which in turn gives a z value of 2. Why don't you just check what 2 sample standard deviations from the sample mean get you?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook