A study was commissioned to find the mean weight of the residents in certain town. The study examined a random sample of 133 residents and found the mean weight to be 165 pounds with a standard deviation of 25 pounds. Use the normal distribution/empirical rule to estimate a 95% confidence interval for the mean, rounding all values to the nearest tenth.
Q. A study was commissioned to find the mean weight of the residents in certain town. The study examined a random sample of 133 residents and found the mean weight to be 165 pounds with a standard deviation of 25 pounds. Use the normal distribution/empirical rule to estimate a 95% confidence interval for the mean, rounding all values to the nearest tenth.
Identify Data Parameters: Identify the sample mean, standard deviation, and sample size. The sample mean (xˉ) is 165 pounds, the standard deviation (s) is 25 pounds, and the sample size (n) is 133 residents.
Calculate Standard Error: Determine the standard error of the mean (SEM). The standard error of the mean is calculated by dividing the standard deviation by the square root of the sample size. SEM=nsSEM=13325SEM≈11.532625SEM≈2.1689 Round to the nearest tenth: SEM≈2.2 pounds
Find Z-Score: Find the z-score that corresponds to a 95% confidence level.For a 95% confidence interval, the z-score is typically 1.96 (this value comes from standard normal distribution tables).
Calculate Margin of Error: Calculate the margin of error (ME) using the z-score and the standard error.ME=z×SEMME=1.96×2.2ME≈4.312Round to the nearest tenth: ME≈4.3 pounds
Determine Confidence Interval Bounds: Calculate the lower and upper bounds of the 95% confidence interval.Lower bound = xˉ−MELower bound = 165−4.3Lower bound ≈160.7 poundsUpper bound = xˉ+MEUpper bound = 165+4.3Upper bound ≈169.3 pounds
Final Confidence Interval: Round the lower and upper bounds to the nearest tenth and state the final 95% confidence interval.The 95% confidence interval for the mean weight of the residents is approximately (160.7,169.3) pounds.
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