Answer:
The 95% confidence interval for the mean of gas mileage for this vehicle is (S - 1.53, S + 1.53), in which S is the mean of the sample of 20.
Step-by-step explanation:
We have that to find our [tex]\alpha[/tex] level, that is the subtraction of 1 by the confidence interval divided by 2. So:
[tex]\alpha = \frac{1 - 0.95}{2} = 0.025[/tex]
Now, we have to find z in the Ztable as such z has a pvalue of [tex]1 - \alpha[/tex].
That is z with a pvalue of [tex]1 - 0.025 = 0.975[/tex], so Z = 1.96.
Now, find the margin of error M as such
[tex]M = z\frac{\sigma}{\sqrt{n}}[/tex]
In which [tex]\sigma[/tex] is the standard deviation of the population and n is the size of the sample.
[tex]M = 1.96\frac{3.5}{\sqrt{20}} = 1.53[/tex]
The lower end of the interval is the sample mean subtracted by M. So it is S - 1.53.
The upper end of the interval is the sample mean added to M. So it is S + 1.53.
The 95% confidence interval for the mean of gas mileage for this vehicle is (S - 1.53, S + 1.53), in which S is the mean of the sample of 20.
