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Subject:  Statistics

99% confidence interval — x̄ = 120, s = 15, n = 100

A larger sample and a higher confidence level — what changes?

Answer 99% CI = (116.136, 123.864)

Solution

  1. Given x̄ = 120, s = 15, n = 100, level = 99%
  2. Critical value z* = 2.576
  3. Standard error SE = s / √n = 15 / √100 = 1.5
  4. Margin of error E = z*·SE = 2.576·1.5 = 3.864
  5. Interval x̄ ± E = (116.136, 123.864)

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