91Ó°ÊÓ

$n=36$and $\stackrel{¯}{x}=63.28$

The formula used:$\stackrel{¯}{x}Â\pm \frac{1\mathrm{σ}}{\sqrt{n}}$

Using Property $1.$, calculate a $68\%$confidence interval for the mean price of all new mobile homes.

From Examples $8.1$and $8.1,n=36$and $\stackrel{¯}{x}=63.28$

Empirical rule:

Property 1: Around $68\%$of the data set is located between $(\stackrel{¯}{x}-s,\stackrel{¯}{x}+s)$

Property 2: Approximately $95\%$of the data set is located between

Property 3: Approximately $99.7\%$of the data set is located between

Using Property $1,$ $68$ percent of the observations are within one standard deviation of the mean on either side.

The $95\%$confidence interval for the population mean is,

$$\begin{gathered} \stackrel{¯}{x}Â\pm \frac{1\mathrm{σ}}{\sqrt{n}}=63.28Â\pm \frac{1(7.2)}{\sqrt{36}} \\ =63.28Â\pm 1.2 \\ =(63.28-1.2,63.28+1.2) \\ =(62.08,64.48) \end{gathered}$$

By considering Property $1,$the $68$percent confidence interval for the mean price of all new mobile homes is $(62.08,64.48)$

As a result, the $\left(\mathrm{μ}\right)$ mean price of all new mobile homes falls within the $68\%$ confidence interval.