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A recent study of 28 city residents showed that the mean of the time they had lived at their present address was 9.3 years. The standard deviation of the population was 2 years. Find the 90% confidence interval of the true mean? Assume that the variable is approximately normally distributed. Show all your stepsVery confused in this exercise I’m self teaching myself

Sagot :

Given that:

- The sample size is 28 city residents:

[tex]n=28[/tex]

- The mean of the time (in years) they had lived at their present address was:

[tex]\mu=9.3[/tex]

- The standard deviation (in years) of the population was:

[tex]\sigma=2[/tex]

Then, you need to use the following formula for calculating the Confidence Interval given the Mean:

[tex]C.I.=\mu\pm z\frac{\sigma}{\sqrt{n}}[/tex]

Where μ is the sample mean, σ is the standard deviation, "z" is the z-score, and "n" is the sample size.

By definition, the z-score for a 90% confidence interval is:

[tex]z=1.645[/tex]

Therefore, you can substitute values into the formula and evaluate:

[tex]C.I.=9.3\pm(1.645)(\frac{2}{\sqrt{28}})[/tex]

You get that the lowest value is:

[tex]9.3-(1.645)(\frac{2}{\sqrt{28}})\approx8.678[/tex]

And the highest value is:

[tex]9.3+(1.645)(\frac{2}{\sqrt{28}})\approx9.922[/tex]

Hence, the answer is:

[tex]From\text{ }8.678\text{ }to\text{ }9.922[/tex]