A recent graduate school study of a random sample of 250 US manufacturing companies determined the average financial report preparation time was 68.04 days with a standard deviation of 35.74 days. Calculate to three decimal places the 95 percent confidence interval for the mean report prep time for all US manufacturing companies. [63.001, 72.008] [63.957, 75.568] [63.505, 72.414] [61.612, 74.468] [63.612, 72.468]

Respuesta :

Answer:

[tex]68.04-1.959\frac{35.74}{\sqrt{250}}=63.618[/tex]    

[tex]68.04+1.959\frac{35.74}{\sqrt{250}}=72.461[/tex]    

And the best option for this case would be

Step-by-step explanation:

Information given

[tex]\bar X=68.04[/tex] represent the sample mean

[tex]\mu[/tex] population mean

s=35.74 represent the sample standard deviation

n=250 represent the sample size  

Confidence interval

The confidence interval for the mean is given by the following formula:

[tex]\bar X \pm t_{\alpha/2}\frac{s}{\sqrt{n}}[/tex]   (1)

The degrees of freedom are given by:

[tex]df=n-1=250-1=249[/tex]

The Confidence level is 0.95 or 95%, and the significance [tex]\alpha=0.05[/tex] and [tex]\alpha/2 =0.025[/tex], and the critical value for this case woud be [tex]t_{\alpha/2}=1.956[/tex]

And replacing we got:

[tex]68.04-1.959\frac{35.74}{\sqrt{250}}=63.618[/tex]    

[tex]68.04+1.959\frac{35.74}{\sqrt{250}}=72.461[/tex]    

And the best option for this case would be