Question

Suppose the weights of tight ends in a football league are normally distributed such that σ2=400. A sample of 11 tight ends was randomly selected, and the weights are given below. Calculate the 95% confidence interval for the mean weight of all tight ends in this league. Round your answers to two decimal places and use ascending order.

Answer 1

Answer:

$217.636-1.96\frac{20}{\sqrt{11}}=205.817$    

$217.636+1.96\frac{20}{\sqrt{11}}=229.455$    

So on this case the 95% confidence interval would be given by (205.82;229.46)    

Step-by-step explanation:

Assuming the following data: Weight 150 169 170 196 200 218 219 262 269 270 271

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".

$\bar X$ represent the sample mean for the sample  

$\mu$ population mean (variable of interest)

$\sigma= \sqrt{400}= 20$ represent the population standard deviation

n=11 represent the sample size  

Solution to the problem

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

$\bar X \pm z_{\alpha/2}\frac{\sigma}{\sqrt{n}}$   (1)

In order to calculate the mean we can use the following formula:  

$\bar X= \sum_{i=1}^n \frac{x_i}{n}$ (2)  

The mean calculated for this case is $\bar X=217.636$

Since the Confidence is 0.95 or 95%, the value of $\alpha=0.05$ and $\alpha/2 =0.025$, and we can use excel, a calculator or a table to find the critical value. The excel command would be: "=NORM.INV(0.025,0,1)".And we see that $z_{\alpha/2}=1.96$

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

$217.636-1.96\frac{20}{\sqrt{11}}=205.817$    

$217.636+1.96\frac{20}{\sqrt{11}}=229.455$    

So on this case the 95% confidence interval would be given by (205.82;229.46)