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dangina [55]
3 years ago
9

The speeds of vehicles traveling on a highway are normally distributed with an unkown population mean and standard deviation. A

random sample of 11 vehicles is taken and results in a sample mean of 65 miles per hour and sample standard deviation of 9 miles per hour. Determine and interpret the 90% confidence interval for the mean speeds of vehicles traveling on the highway.
Mathematics
1 answer:
Maksim231197 [3]3 years ago
3 0

Answer:

The 90% confidence interval would be given by (60.09;69.91)    

We are 90% confident that the true mean for the speeds of vehicles traveling on a highway is between 60.09 and 69.91 miles per hour.

Step-by-step explanation:

1) Previous concepts

A confidence interval is "a range of values that’s likely to include a population value with a certain degree of confidence. It is often expressed a % whereby a population means lies between an upper and lower interval".

The margin of error is the range of values below and above the sample statistic in a confidence interval.

Normal distribution, is a "probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean".

\bar X =65 represent the sample mean for the sample  

\mu population mean (variable of interest)

s=9 represent the sample standard deviation

n=11 represent the sample size  

2) Confidence interval

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

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

In order to calculate the critical value t_{\alpha/2} we need to find first the degrees of freedom, given by:

df=n-1=11-1=10

Since the Confidence is 0.90 or 90%, the value of \alpha=0.1 and \alpha/2 =0.05, and we can use excel, a calculator or a table to find the critical value. The excel command would be: "=-T.INV(0.05,10)".And we see that t_{\alpha/2}=1.81

Now we have everything in order to replace into formula (1):

65-1.81\frac{9}{\sqrt{11}}=60.09    

65+1.81\frac{9}{\sqrt{11}}=69.91

So on this case the 90% confidence interval would be given by (60.09;69.91)    

We are 90% confident that the true mean for the speeds of vehicles traveling on a highway is between 60.09 and 69.91 miles per hour.

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