High School

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Suppose a random sample of 40 American men is drawn and the weights of the men measured. If the sample mean is 182 lbs. and sample standard deviation is 18.4 lbs., construct a 90% confidence interval for the mean weight of the population of American men. Round each of the endpoints of your interval to one decimal place.

Option A (172.4, 188.6)
Option B none of the others
Option C (176.2, 184.6)
Option D (177.2, 186.8)
Option E (175.2, 189.2)

Answer :

To construct a 90% confidence interval for the mean weight of the population of American men based on the given sample data, we'll use the formula for a confidence interval for a population mean when the sample size is large enough (n ≥ 30), using the sample mean, sample standard deviation, and the standard normal distribution (Z-distribution).

Here are the step-by-step calculations:

  1. Identify the Sample Statistics:

    • Sample mean ([tex]\bar{x}[/tex]): 182 lbs
    • Sample standard deviation (s): 18.4 lbs
    • Sample size (n): 40
  2. Determine the Confidence Level and Z-Score:

    • We're constructing a 90% confidence interval.
    • For a 90% confidence level, the Z-score is approximately 1.645 (from standard Z-tables).
  3. Calculate the Standard Error (SE):
    [tex]SE = \frac{s}{\sqrt{n}} = \frac{18.4}{\sqrt{40}} \approx 2.91[/tex]

  4. Compute the Margin of Error (ME):
    [tex]ME = Z \times SE = 1.645 \times 2.91 \approx 4.79[/tex]

  5. Construct the Confidence Interval:

    • Lower bound: [tex]\bar{x} - ME = 182 - 4.79 \approx 177.2[/tex]
    • Upper bound: [tex]\bar{x} + ME = 182 + 4.79 \approx 186.8[/tex]

Therefore, the 90% confidence interval for the mean weight of the population of American men is approximately [tex](177.2, 186.8)[/tex].

The correct multiple-choice option is Option D (177.2, 186.8).

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