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If n=30, 𝑥¯(x-bar)=35, and s=7, construct a confidence interval at a 99% confidence level. Assume the data came from a normally distributed population.Give your answers to one decimal place. < 𝜇 <

Question

If n=30, 𝑥¯(x-bar)=35, and s=7, construct a confidence interval at a 99% confidence level. Assume the data came from a normally distributed population.Give your answers to one decimal place. < 𝜇 <

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Solution

To construct a confidence interval for the population mean (μ) at a 99% confidence level, given that the sample size (n) is 30, the sample mean (x̄) is 35, and the sample standard deviation (s) is 7, follow these steps:

  1. Identify the critical value (z) for a 99% confidence level:* Since the sample size is less than 30, we use the t-distribution. For a 99% confidence level and degrees of freedom (df) = n - 1 = 30 - 1 = 29, we look up the t-value in the t-distribution table. The critical value (t*) for 29 degrees of freedom at a 99% confidence level is approximately 2.756.

  2. Calculate the standard error (SE) of the mean: SE=sn=7301.278 SE = \frac{s}{\sqrt{n}} = \frac{7}{\sqrt{30}} \approx 1.278

  3. Calculate the margin of error (ME): ME=t×SE=2.756×1.2783.5 ME = t^* \times SE = 2.756 \times 1.278 \approx 3.5

  4. Construct the confidence interval: Lower limit=xˉME=353.5=31.5 \text{Lower limit} = x̄ - ME = 35 - 3.5 = 31.5 Upper limit=xˉ+ME=35+3.5=38.5 \text{Upper limit} = x̄ + ME = 35 + 3.5 = 38.5

Therefore, the 99% confidence interval for the population mean (μ) is: 31.5<μ<38.5 31.5 < \mu < 38.5

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