Answer:
The 99% confidence interval would be given (11.448;14.152).
Step-by-step explanation:
1) Important concepts and notation
A confidence interval for a mean "gives us a range of plausible values for the population mean. If a confidence interval does not include a particular value, we can say that it is not likely that the particular value is the true population mean"
represent the sample deviation
represent the sample mean
n =1003 is the sample size selected
Confidence =99% or 0.99
represent the significance level.
2) Solution to the problem
The confidence interval for the mean would be given by this formula
![\bar X \pm z_{\alpha/2} \frac{s}{\sqrt{n}}](https://tex.z-dn.net/?f=%5Cbar%20X%20%5Cpm%20z_%7B%5Calpha%2F2%7D%20%5Cfrac%7Bs%7D%7B%5Csqrt%7Bn%7D%7D)
We can use a z quantile instead of t since the sample size is large enough.
For the 99% confidence interval the value of
and
, with that value we can find the quantile required for the interval in the normal standard distribution.
![z_{\alpha/2}=2.58](https://tex.z-dn.net/?f=z_%7B%5Calpha%2F2%7D%3D2.58)
And replacing into the confidence interval formula we got:
![12.8 - 2.58 \frac{16.6}{\sqrt{1003}}=11.448](https://tex.z-dn.net/?f=12.8%20-%202.58%20%5Cfrac%7B16.6%7D%7B%5Csqrt%7B1003%7D%7D%3D11.448)
![12.8 + 2.58 \frac{16.6}{\sqrt{1003}} =14.152](https://tex.z-dn.net/?f=12.8%20%2B%202.58%20%5Cfrac%7B16.6%7D%7B%5Csqrt%7B1003%7D%7D%20%3D14.152)
And the 99% confidence interval would be given (11.448;14.152).
We are confident that about 11 to 14 are the number of books that the people had read on the last year on average, at 1% of significance.