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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

    dm.jpg

    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

    LCKurtz

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    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?
     
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