Question

A researcher takes a simple random sample of 83 homes in a city and finds that the mean square footage is 1628 with a standard deviation of 243 square feet. What is the 90% confidence interval for the mean square footage of all the homes in that city?

Answer 1

Answer: (1583.63, 1672.37)

Step-by-step explanation:

Given : Sample size : n= 83

Sample mean : $\overline{x}=1628$

Sample standard deviation : $\sigma=243$

The population standard deviation$(\sigma)$ is unknown .

The confidence interval for population mean :

$\overline{x}\pm t_{\alpha/2}\dfrac{s}{\sqrt{n}}$

For 90% confidence , significance level =$\alpha=1-0.90=0.10$

Using t-distribution table , Critical t-value = $t_{(\alpha/2, n-1)}=t_{0.05,82}=1.6636$

, where n-1 is the degree of freedom.

Now ,  90% confidence interval for the mean square footage of all the homes in that city will be :-

$1628\pm (1.6636)\dfrac{243}{\sqrt{83}}\\\\ 1628\pm (1.6636)(26.672715)\\\\\\\\\approx1628\pm 44.37\\\\=(1628- 44.37,\ 1628+ 44.37)\\\\=(1583.63,\ 1672.37)$

Hence, the 90% confidence interval for the mean square footage of all the homes in that city = (1583.63, 1672.37)